Evaluation of Ethiopian White Cumin (Trachyspermum ammi L.) accessions for agronomic and quality traits in the Central Highlands of Ethiopia

Abstract

Experiments under field conditions were conducted in the Meher season from mid-July to December 2019 and 2020 at Kulumsa and Arsi Robe, Southeast Ethiopia. The study intended to evaluate white cumin accessions for agronomic and quality traits. Fifteen genotypes were laid out in a randomized complete block design in three replications. The analysis of variance pooled over the two locations and years showed highly significant differences (p < 0.001) for ten agronomic and two quality traits. The top seven accessions, namely, Shirka 001/2007, Sole-007, Akiya-2007, Tena-2007, Bale-2007, Shirka-2007, and Silingo-2007, were the high yielders compared to Takusa-1 and Dembia-1 cultivars and could be advanced to the national variety trial. The highest essential oil content was recorded from the Dembia-1 (6.5%) cultivar, followed by Takusa-1 (6.42%), Shirka-2007 (6.23%), Sagure-2005 (6.23%), and Gedgeda-026 (6.23%), while the highest oleoresin content was recorded from Takusa-1 (28.3%), Gedgeda-026 (27.73%), and Shirka 001/2007 (27.54%). Shirka-2007 and Shirka 001/2007 matured earlier in 144 and 153.58 days, respectively, and could be used in crossing blocks. There was strong and positive association between the number of umbels plant⁻¹ and the number of umbellets umbel⁻¹ (r = 0.98***), the days to 50% flowering and physiological maturity (r = 0.9***), the days to 50% emergency and flowering (r = 0.89***), the seed yield plant⁻¹ and the 1000 seed weight (r = 0.87***), and the days to 50% maturity and the number of umbels plant⁻¹ (r = 0.86***). Hence, stable accessions in potential growing regions of Ethiopia could be selected for the release.

Keywords:

• Ajwain
• correlation
• essential oil
• oleoresin

REVIEWING EDITOR:

• Manuel Tejada, University of Seville, Spain

SUBJECTS:

• Agriculture & Environmental Sciences
• Soil Sciences
• Botany

1. Introduction

Ethiopia has the potential to produce and export spices; however, production, productivity, and quality are affected by enormous factors like cultivation practices, post-harvest handling losses, and diseases (Hordofa &Tolossa, 2020). Black cumin, fenugreek, coriander, and white cumin (ajwain) are the seed spices mainly cultivated in the highland areas of Arsi, Bale, Gondar, Shewa, and Wello in Ethiopia for their seeds (Habetewold et al., 2017; Tesfa et al., 2017; Tesfaye, 2017; Girma et al., 2022).

Trachyspermum ammi L. Sprague is an annual cross-pollinated (Endalkachew et al., 2020) plant with a somatic chromosome number of 2n = 18. The flowers are self-fertile, but cross-pollination occurs through insects. It belongs to the Apiaceae (Umbelliferae) family. It is an herbaceous plant with white flowers and small brownish fruit growing in the east of India, Iran, Pakistan, Egypt, around the Mediterranean Sea, and Ethiopia (Dalkani et al., 2012; Tomar & Malik, 2014; Girma et al., 2016; Habetewold et al., 2017). It is one of the most dominantly cultivated seed spices in Ethiopia for consumption and commercial purposes from mid-to-high attitudes from 1750 to 2200 m.a.s.l. (Habetewold et al., 2017; Tesfa et al., 2017; Girma et al., 2022). It is known by different names: Caraway, Ajwain, and Bishop’s weed are the commonly known names. In Ethiopia, it is named differently in diverse languages: nech azmud (Amharic) and abeshuda adi (Afan Oromo) (Goettsch, 2009; Alemnew, 2021).

The Ethiopian variety of white cumin accumulates up to 9% essential oil, of which 55% is the volatile component thymol (Amare & Mekuria, 2013), making it valuable for use in personal hygiene, cooking, and medicine (Ravindran & Balachandran, 2004). The Indian white cumin has been reported to accumulate 2.5–5% essential oil in its seed (Raghavan, 2007); however, the two registered cultivars of white cumin (ajwain) varieties, Takusa-1 and Dembia-1, had essential oil contents of 6.42% and 6.5%, which are responsible for the characteristic aroma, and oleoresin contents of 28.3% and 26.55%, respectively. It is useful for medicinal and culinary purposes (Ashraf & Orooj, 2006). In Ethiopia, it is often used in ‘Berbere’, where it tends to diminish the hotness (Hedberge et al., 2003), for bread, ‘katikala’ (Jansen, 1981), ‘shamita’ (Mogessie & Tetemke, 1995), traditional Ethiopian stews, ‘wot’, at the start and end of wot preparation as ‘Makulaliya’ and ‘ Mekelesha’, respectively, and for butter preservation.

Research on white cumin or caraway was previously reported on agronomic practices, genetic structure, stability, and diversity; however, most studies focused on its essential oil composition (Nath et al., 2008; Chauhan et al., 2012; Zarshenas et al., 2014; Giridhar et al., 2016; Heidari et al., 2016; Pooja et al., 2023; Trivedi et al., 2023). In Ethiopia, the studies on Ethiopian white cumin focused mainly on its essential oil, medicinal properties, agronomic practices, genetic variability assessment, and multi-environment stability analysis (Amare & Mekuria, 2013; Seid et al., 2013; Tesfaye, 2017; Endalkachew et al., 2020).

Limited efforts have been made to understand the genetic differences and evaluation of accessions, genetic improvement, heritability, and the 5% selection intensity of target traits. In white cumin, conventional methods based on the selection of desirable genotypes have responded well to yield enhancement and quality traits; the evolution of the collected genotypes from different parts of the country is necessary for performing selection cycles in a population. So far, only Takusa-1 and Dembia-1 cultivars of white cumin have been registered in Ethiopia (Anonymous, 2022), it is one of the neglected areas of the research system where intensive research activities have not been conducted. Even though the initial evaluation of the germplasm has shown that the variability is enormous in this crop, the generation of information on those genotypes could help to advance to the next breeding stage of the crop and variety registration. Further studies are mandatory to fill the existing gaps and to develop high-yielding varieties with considerable quality traits. Thus, the study aimed to evaluate white cumin accessions for agronomic and quality traits.

2. Materials and methods

2.1. Study sites

The study sites are located 165 and 182 km South-east of Addis Ababa, Ethiopia. Kulumsa Agricultural Research Center (KARC) and Arsi Robe research sites are situated at 8° 02′ N and 09° 36′ N and 39° 10′ E and 39° 08′ E latitude and longitude at an elevation of 2210 and 2435 m.a.s.l., respectively. The studies were conducted in Meher season from 15^th July to December in 2019 and 2020. The areas receive an average annual rainfall of 832 and 798.3 mm, respectively. The minimum and maximum temperatures were 10 °C and 23.20 °C and 10.5 °C and 25 °C, respectively. Eutric Vertisols with high water retention capacity are the dominant soils at Arsi Robe, while Vertic Luvisols are at the Kulumsa site (Abu et al., 2019).

2.2. Experimental materials and design

Thirteen white cumin accessions, out of 150 altogether, were used as experimental material in the previous observation nursery and advanced to the preliminary variety trial. These accessions were originally collected from various parts of Ethiopia (Table 1) and deposited at KARC. In addition, two released cultivars, Takusa-1 (Gondar 027/2001) and Dembia-1 (Gondar 023/2000), registered by the Gonder Agricultural Research Center after testing their performance at Takusa, Dembia, Chafe, DebreZeit, Kulumsa, and Asosa (Endalkachew et al., 2020; Anonymous, 2022), were included as a standard check. Table 1 displays the list of white cumin accessions together with their passport information. Three replications and a randomized complete block design were used to set up the experiment. Each experimental unit had a 3.6 m² plot with four 2.4 m² harvestable (net plot) rows. The row spacing was 30 cm, and 6 kg of seeds per hectare was the consistent seed rate drilled.

Table 1. List of the white cumin (T. ammi) accessions with their passport data.

Accessions	Region	Zone	Latitude (N)	Longitude (E)	Altitude
Tena-2007	Oromia	Arsi	7° 45’	39° 25’	1800–4100
Akiya-2007	Oromia	Arsi	7° 45’	39° 25’	1950
Shirka-2007	Oromia	Arsi	7° 37’	39° 30’	2353
Shirka 001/2007	Oromia	Arsi	7° 37’	39° 30’	2400
Bale-2007	Oromia	Bale	6° 59’	40°30’	1650
Silingo-2007	Oromia	Arsi	08°10’	39°09’	2300
Sagure-2005	Oromia	Arsi	07°45’	39°09’	2568
G-002	Oromia	Bale	6° 59’	40°30’	1670
Sole-007	Oromia	Arsi	7° 45’	39° 25’	Not available
Tereta-004	Oromia	Arsi	7° 45’	39° 25’	Not available
Gedgeda-026	Oromia	Arsi	7° 45’	39° 25’	Not available
Robe-2007	Oromia	Arsi	09° 36’	39° 08’	2435
Sagure-2007	Oromia	Arsi	07°45’	39°09’	2568
Takusa-1	Amhara	Semen Gonder	12°10’	37°01’	1840
Dembia-1	Amhara	Semen Gonder	12°30’	37° 33’	1920

E= East and N= North.   

2.3. Data collection

Data were collected on a plot-by-plant basis. So the variables were gathered from ten randomly selected plants from the middle four rows of each plot. These traits are expressed below.

2.3.1. Phenological data

Days to 50% emergency: number of days from the date of sowing to when 50% of the seedlings appeared above ground level.

Days to 50% flowering: the days from sowing to 50% of the plants in a plot get bloomed.

Days to 90% physiological maturity: the number of days from the date of sowing to when the plant changed from a dark green to a brown color, 90% of the umbellets changed to brownish, and the fruits started to wither.

2.3.2. Agronomic, yield and yield related traits

Plant height: an average height (cm) was measured from 10 randomly selected plants from ground level to the tip of the umbels.

Number of primary branches plant⁻¹: the number of primary branches was recorded by counting branches from 10 plant parts raised from the main stem as primary branches.

Number of umbels plant⁻¹: the average number of effective umbels from the ten randomly selected plants was counted.

Number of umbellets umbel⁻¹: the average number of umbellets was counted from 10 randomly selected plants of effective 5 umbels from each plant.

Seed yield plant⁻¹ (g): the average seed weight of 10 randomly selected and tagged plants was taken from the middle four rows excluding the border rows to avoid the border effect.

Seed yield ha⁻¹ (kg): seed yield was determined by harvesting plants from the four middle rows from a net area of 2.4 m² (2 m × 1.2 m) to avoid border effects. Seeds, which were obtained from the corresponding net plot, were cleaned manually. After sun-dried and adjusted to 9.5% moisture content, it was weighed in grams by using a sensitive balance and recorded values of seed yield were converted to kg ha⁻¹.

Thousand seed weight (g): one thousand seeds were chosen at random and tallied from each experimental unit. The seeds were then sun-dried, measured and adjusted to a moisture content of 9.8% and their weight was expressed in grams.

2.3.3. Quality traits

Determination of essential oil and oleoresin contents (%):

Soxhlet extractor was used to remove the oleoresin from the white cumin seeds. Before being used, the seeds of each accession were kept in an amber glass screw-cap container at room temperature after being coarsely crushed to 30 g each using 300 ml of hexane solvent for 12 hours as steps followed by Dinagaran et al. (2017); Biruk and Sileshi (2019); Fekadu and Gizaw (2023). After that, steam is pumped through the ground seeds in a distillation chamber. The essential oil vaporizes due to the steam and ascends into a condenser where it cools and re-condenses into a liquid state (Fekadu & Gizaw, 2023). The resulting liquid is a concentrated form of essential oil, which can be further processed to remove water or remaining impurities. The samples were replicated three times and the solvent was removed using a rotary evaporator operating at 45 °C and the final trace of solvent was removed under a stream of nitrogen.

2.4. Statistical analysis

2.4.1. Analysis of variance

The lm function of the stats package in R software (Anonymous, 2020) was utilized to apply the data collected for each trait for analysis of variance (ANOVA), using the methodology outlined in Gomez and Gomez (1984). The assumptions of ANOVA for each data point were made before the analysis, and pooled data analysis over locations and years was carried out for all traits. A least significant difference was used to compare the mean performance of ajwain (white cumin) accessions at a 5% level of significance.

2.4.2. Pearson correlation analysis

The graphical outputs of the Pearson correlation matrix were piloted using ggcorrplot using the ggplot2 package of R software (Anonymous, 2020).

3. Results and discussion

3.1. Analysis of variance

All of the phenological, agronomic, yield, and quality characteristics included in the study showed highly significant differences (P < 0.001) when the combined analysis of variance (ANOVA) over location and year was performed (Table 2). This outcome indicated that there were significant variations between the white cumin accessions. Similarly, Seid et al. (2013) in Mersa, North Wollo, demonstrated significant variations among 36 Ethiopian caraway accessions for days to 50% emergency, flowering, and maturity, number of primary and secondary branch plant⁻¹, plant height, yield of seeds, and 1000 seed weight. Significant variations in seed yield were noted by Endalkachew et al. (2020) and Heidari et al. (2016) for 12 caraway genotypes collected from Ethiopia and 117 ajowan (Trachyspermum ammi L.) accessions collected in Iran, respectively. In agreement with the present study, Pooja et al. (2023) reported significant differences between 28 ajwain (Trachyspermum ammi L. Syn. Carum copticum) genotypes for days to germination, plant height, days taken for commencement of 50% flowering, the days to harvest, the number of umbels in an individual plant, umbellets umbel⁻¹, seed weight, essential oil, and oleoresin content in Karnataka, India. Endalkachew et al. (2020) also reported significant variations between the Ethiopian caraway genotypes for days to 50% physiological maturity, plant height, number of branches plant⁻¹, umbels plant⁻¹, and seed yield (kg ha⁻¹). The pooled ANOVA (Table 2) for seed yield of 15 Ethiopian white cumin accessions studied across two environments indicated that there were no significant differences in the effect of accession × environment interaction, unlike Endalkachew et al. (2020) reported significant differences of G × E for 12 Ethiopian caraway genotypes across eight environments.

Table 2. Mean squares from pooled analysis of variances at Kulumsa and Robe Arsi and from 2019 to 2020 years for 12 traits of white cumin genotypes.

S.V	Traits
	DF	DE	DFL	DM	PH	NPBP	NUP	NULTSP	SYP	SYPH	TSW	EOC (%)	ORC (%)
Genotype	14	46.43***	272.13***	2227.84***	131.12***	13.55***	1044.79***	6037.30***	1.17***	260490.44***	1.13***	2.43***	23.60***
Year	1	42.05 ^ns	1608.02**	7018.76***	1006.76***	48.06***	3048.17***	16240.59***	0.67*	1415404.56***	4.28***	0.19***	5.30***
Location	1	136.94***	2026.76**	3591.20***	17611.28***	19.70***	8584.04***	20845.11***	146.46***	897945.15***	0.07 ^ns	0.7***	6.96***
Block (Location)	4	9.59 ^ns	90.78***	7.61 ^ns	50.43*	1.91*	1436.61***	7530.80***	0.24 ^ns	136830.53*	0.29 ^ns	0.002*	0.77***
Block (Year × Location)	4	17.53 ^ns	50.11*	1.78 ^ns	0.67 ^ns	0.09 ^ns	80.04 ^ns	385.19 ^ns	0.06 ^ns	34108.62 ^ns	0.22 ^ns	0.005***	0.33**
Genotype × Location	14	8.51 ^ns	41.66**	542.77***	3.23 ^ns	25.00***	1263.98***	8014.63***	0.93***	279910.35***	0.31*	0.01***	1.03**
Year × Location	1	8.45 ^ns	12.80 ^ns	5.00 ^ns	208.42**	7.89**	989.27**	5287.91**	0.82*	2817646.00***	0.06 ^ns	0.0003 ^ns	0.04 ^ns
Year × Genotype	14	110.00***	107.24***	322.61***	25.93 ^ns	2.80***	61.53 ^ns	4453.77 ^ns	0.01***	34764.22 ^ns	0.26 ^ns	0.002**	0.20***
Year × Genotype × Location	14	6.31 ^ns	10.25 ^ns	17.86 ^ns	31.21 ^ns	1.85**	96.90 ^ns	506.25 ^ns	0.02 ^ns	61243.02 ^ns	0.80 ^ns	0.0002 ^ns	0.05 ^ns
Error	112	11.74	15.55	22.07	19.02	0.70	125.72	642.60	0.12	5494913.42	0.16	0.001	0.06
Mean		26.94	105.10	180.94	60.10	6.22	40.86	96.63	1.29	1168.35	1.54	5.85	26.2
CV (%)		12.72	3.75	2.60	7.26	13.43	27.44	26.23	26.96	18.96	25.9	0.46	0.9
R^2 (%)		67.20	85.48	95.64	91.07	89.80	79.08	79.69	92.95	72.82	63.98	99.76	98.32
F –value		3.96	17.51	100.95	6.90	19.42	8.31	9.40	9.64	5.31	7.16	3309	424.54

Ns= not significantly different; * = significant at P < 0.05, ** = p < 0.01, *** = P < 0.001.

S.V= sources of variation, R2= coefficient of determination, CV= coefficient of variation , DE= days to 50% emergency, DF= degrees of freedom, DFL= days to 50% flowering, DM= days to 90% physiological maturity, PH= plant height (cm), NPBP= number of primary branch plant⁻¹, NUP= number of umbels plant⁻¹, NULTSP= number of umbellets umbel⁻¹, SYP= seed yield plant⁻¹ SYPH: seed yield (kg ha⁻¹), TSW= thousand seed weight (g), EOC= Essential oil content (%), ORC= oleoresin content(%).

3.2. Mean performance of white cumin accessions for phenological parameters

Based on the pooled mean values of Ethiopian white cumin accessions, Shirka 001/2007 takes 23 days to emerge 50% of the sown seeds per plot, whereas Tereta-004 appears later, in 30.17 days (Table 3). Robe-2007, Tereta-004, and Sagure-2007 were late-blooming accessions that required mean days of 111.33, 110.25, and 108.33, respectively. The first three early flowering accessions were Shirka-2007 (92.92 days), Shirka 001/2007 (99.33), and Dembia-1 (99.92 days). Shirka-2007 and Shirka 001/2007 were the early maturing white cumin accessions in the current study that could be included in the future hybridization program of the crop for earliness, and those accessions matured in 144 and 153.58 days, respectively, with lower seed filing periods. In line with this result, Seid et al. (2013) reported varied days to 50% emergency (13.3–17.3 days) with a grand mean value of 15.3 ± 0.9, 79.7–88.8 days to bloom 50% of the Ethiopian Caraway accessions, and 110–115.3 days to set fruits. Heidari et al. (2016) reported the highest and lowest values of days to 50% and 100% flowering for 117 ajowan accessions of 25 ajowan populations collected from different regions in Iran by mean values of 164.6 and 115.6 days and 123.66 and 170.33, respectively. Endalkachew et al. (2020) also outlined mean days to 50% flowering and 50% of physiological maturity from 87.72–91.83 and 157.17–159.28 days for 12 Ethiopian caraway accessions tested in 6 potential growing areas of white cumin in the country, respectively.

Table 3. Mean performances of white cumin genotypes for 10 agronomic and 2 quality traits evaluated at Kulumsa and Arsi Robe in 2019 and 2020.

Accessions	DE	DFL	DM	PH	NPBP	NUP	NULTSP	SYP	SYPH	TSW	EOC (%)	ORC (%)
Tena-2007	26.83^b-e	105.92 ^cd	185.25 ^cd	58.66^d-g	6.50^b	37.86^bcd	88.64^c-f	1.85^a	1262.51^a-d	2.21^a	5.64^f	23.19^l
Akiya-2007	26.83^b-e	106.50 ^cd	185.42 ^cd	60.65^cde	5.24^ef	29.66^de	68.50^f	1.28^def	1313.48^abc	1.38^def	5.54^g	26.05^h
Shirka-2007	23.67^fg	92.92^g	144.00^h	57.94^efg	5.13^f	55.47^a	126.96^b	1.23^ef	1225.62^bcd	1.47^cde	6.23^c	26.25^g
Shirka 001/2007	23.00^g	99.33^f	153.58^g	55.53^g	6.00 ^cd	59.89^a	147.59^a	0.81^gh	1412.43^a	1.16^ef	5.64^f	27.54^c
Bale-2007	27.17^a-e	106.00 ^cd	185.17^cde	64.69^ab	7.45^b	38.32^bcd	88.91^c-f	1.55^bcd	1229.51^a-d	1.65 ^cd	5.44^h	26.94^d
Silingo-2007	26.33^c-f	104.83^de	183.17^cde	57.88^efg	6.07 ^cd	40.77^bc	96.10 ^cd	0.89^gh	1220.29^bcd	1.07^f	5.24^j	26.35^g
Sagure-2005	26.33^c-f	105.75 ^cd	181.42^ef	58.18^efg	5.52^def	43.98^b	103.04^c	1.20^ef	968.38^fg	1.56 ^cd	6.23^c	25.53^j
G-002	27.75^a-e	108.2^abc	187.12^bc	62.82^bc	5.31^ef	34.76^cde	81.31^def	1.71^ab	1009.91^efg	2.01^bc	5.34^i	25.85^i
Sole-007	28.00^a-e	107.42^bcd	187.75^bc	61.80^bcd	5.08^f	39.00^bc	93.00^cde	1.37^cde	1370.36^ab	1.47^cde	5.14^k	23.49^k
Tereta-004	30.17^a	110.25^ab	192.08^a	63.36^bc	7.20^b	55.27^a	130.91^ab	0.79^h	996.95^efg	1.09^f	6.13^d	26.74^e
Gedgeda-026	29.17^ab	107.50^bcd	188.00^bc	59.87^c-f	6.34^c	39.08^bc	83.85^c-f	1.32^def	1084.79^efg	1.58 ^cd	6.23^c	27.73^b
Robe-2007	28.92^ab	111.33^a	189.67^ab	58.06^efg	5.82^cde	35.37^d-e	82.72^c-f	1.31^def	926.88^g	1.57 ^cd	5.93^e	25.55^j
Sagure-2007	28.58^abc	108.33^abc	189.83^ab	67.40^a	5.48^def	34.54^cde	82.66^c-f	1.38^cde	1152.81^cde	1.54 ^cd	6.13^d	26.94^d
Takusa-1	25.42^efg	102.25^ef	180.75^f	58.78^efg	8.73^a	41.20^bc	102.33	1.62^abc	1132.17^def	1.58 ^cd	6.42^b	28.30^a
Dembia-1	25.92^def	99.92^f	180.00^f	56.44^fg	7.40^b	27.78^e	72.90^ef	1.08^fg	1219.50^bcd	1.72^bc	6.50^a	26.55^f
LSD	2.77	3.19	3.80	3.53	0.68	9.07	20.51	0.28	179.17	0.32	0.02	0.19

Means followed by the same letter/s are not significantly different. LSD= least significant difference, DE= days to 50% emergency, DFL= days to 50% flowering, DM= days to 90% physiological maturity, PH= plant height (cm), NPBP= number of primary branch plant⁻¹, NUP= number of umbels plant⁻¹, NULTSP= number of umbellets umbel⁻¹, SYP= seed yield plant⁻¹ SYPH= seed yield (kg ha⁻¹), TSW= thousand seed weight (g), EOC= Essential oil content (%), ORC= oleoresin content (%).

3.3. Mean performance of agronomic, yield and yield related traits

The highest pooled mean values of plant height were recorded from Sagure-2007 (67.4 cm) followed by Bale-2007 (64.69 cm) and Tereta-004 (63.36 cm), while the shortest plant height was recorded from Shirka 001/2007 (55.53 cm) (Table 3). In accordance, the longest mean values of plant height (89.33 cm) were reported by Heidari et al. (2016) in Iran. In Ethiopia, Endalkachew et al. (2020) reported 64.72 cm height for the caraway genotype collected from Adet, northwestern Ethiopia and the shortest plant height (59.61 cm) for the genotype from Gonder.

The highest number of primary branches plant⁻¹ (8.73) was found from Takusa-1 and the number of umbels plant⁻¹ and effective umbellets umbel⁻¹ with the mean values of 59.89 and 147.59 for Shirka 001/2007, respectively (Table 3). Comparable results in the number of branches plant⁻¹ were also reported in Caraway by other researchers, such as 7.99 to 9.53 (Endalkachew et al., 2020) and 6.33 to 13.16 (Heidari et al., 2016). As displayed in Table 3, Tena-2007 produced the highest seed yield plant⁻¹ (1.85 g), followed by G-002 (1.71 g) and Takusa⁻¹ (1.62 g); conversely, Tereta-004 was low yielder accession.

Seed yield is an intricate quantitative trait and considerable variations in seed yield are attributed to genetic character and the response of accessions to agro-climatic conditions. An increase in seed yield among white cumin accessions could be attributed to enhanced growth factors which positively correlated to yield. Seed yield mainly depends on the total number of branches in a plant, number of umbels in a plant, number of umbellets in an umbel, number of seeds in an umbel and thousand seed weight. It is also associated with better accumulation of dry matter and storage of photosynthesis products.

The first seven high-yielder accessions were: Shirka 001/2007 (1412.43 kg ha⁻¹), Sole-007 (1370.36 kg ha⁻¹), Akiya-2007 (1313.48 kg ha⁻¹), Tena-2007 (1262.51 kg ha⁻¹), Bale-2007 (1229.51 kg ha⁻¹), Shirka-2007 (1225.62 kg ha⁻¹), and Silingo-2007 (1220.29 kg ha⁻¹). Those accessions were advanced to the national variety trial for multi-location and year-long trials in the potential growing regions of the country. However, because of the advantages of Gedgeda-026 and Sagure-2007’s essential oil and oleoresin content, Tena-2007 and Shirka-2007 were dropped and replaced. Previously, Amare and Mekuria (2013) asserted that the rise in white cumin seed production was driven by an increase in nitrogen levels, which rose from 666 to 957 kg ha⁻¹ with no application to 100 kg ha⁻¹. Similarly, Nath et al. (2008) showed that spacing and nitrogen levels altered the mean seed yields of ajowan (Trachyspermum ammi), which fluctuated between 3.23 and 5.66 g plant⁻¹. Rahman et al. (2023) also reported an augmentation in the seed yield of ajowan from 786.15 to 987.48 kg ha⁻¹ as the seed rate increased from 3 kg ha⁻¹ up to 4.5 kg ha⁻¹ in Bangladesh tested for two consecutive years. Ajwain genotypes exhibit notable variations in seed production, as previously shown by a number of studies, including Giridhar et al. (2016), and Pooja et al. (2023). Heidari et al. (2016) also distinguished the varied yield among 25 ajowan populations from 132–453 gm⁻², and in line with the present study, Endalkachew et al. (2020) stated higher yields of caraway for Takusa-1 and Dembia-1 among 12 genotypes tested across environments in Ethiopia.

Tena-2007 (2.21 g) was the accession with the highest 1000 seed weight, followed by G-002 (2.01 g) and Dembia-1 (1.72 g). The results of this study show a higher thousand seed weight in contrast to the results of Amare and Mekuria (2013), who reported a 1000 seed weight of 1 g while testing the interaction effect of nitrogen and phosphorus on thousand seed weight at Mersa, in the north-eastern parts of Ethiopia. Heidari et al. (2016) also noted a thousand seed weights with a mean value of 0.58–0.96 g among the 25 Ajowan populations.

3.4. Mean performance white cumin accessions for essential oil and oleoresin contents

The data on the essential oil and oleoresin content showed significant variation among the white cumin accessions. The quality of white cumin seeds is a prime aspect that determines their premium cost in the market. The mean performance of essential oil and oleoresin contents of Ethiopian white cumin accessions is presented in Table 3. Dembia-1 (6.5%) had the highest essential oil content, followed by Takusa-1 (6.42%), Shirka-2007 (6.23%), Sagure-2005 (6.23%), and Gedgeda-026 (6.23%). Takusa-1 (28.3%), Gedgeda-026 (27.73%), and Shirka 001/2007 (27.54%) had the highest oleoresin content. This might be a result of how environment and genotype interact and how the maturity of the crop influences the amount of essential oils and oleoresin. Genotypes with comparable yield and quality trait benefits above standard checks, such as Dembia-1 and Takusa-1, were advanced to the national variety trial in the potential growing areas of upcoming breeding programs. The results are in line with previous research conducted by Saxena et al. (2016), Subramaniyan et al. (2019), and Pooja et al. (2023). Since starch is a primary metabolite, it may have an impact on how essential oils and other secondary metabolites build up. Due mostly to their high starch content, accessions with greater seed size could have lower essential oil content.

3.5. Pearson’s correlation analysis

To improve crop yield or plant structure, selection must be based on the association of related features, which measures the interrelationships between different plant traits and identifies constituent traits on which breeding can be based to improve the seed yield of crops (Endalkachew et al., 2020; Rahman et al., 2023). It may be easier to boost seed yield by increasing the yield components of superior cultivars (Rahman et al., 2023). The pooled correlations over years and locations are presented in Figure 1. The correlation analysis displayed a strong and positive association between the number of umbels plant-1 and the number of umbellets umbel-1 (r = 0.98***), the days to 50% flowering and physiological maturity (r = 0.9***), the days to 50% emergency and flowering (r = 0.89***), the seed yield plant-1 and the 1000 seed weight (r = 0.87***), and the days to 90% physiological maturity and the number of effective umbels plant-1 (r = −0.65**). The negative but strong link between the days to 90% physiological maturity and the number of effective umbels plant⁻¹ could be due to the decrease in the number of effective tillers as the days to maturity lengthened and the lack of residual moisture at maturity, which simultaneously results in a decline in the yield per plant. Seed yield (kg ha⁻¹) was negatively correlated with days to 50% emergency (r = −0.55*). This might be the tardy emergency of seeds, which could result in an extended period of seed filing and a drop in seed yield due to terminal stress. The results are consistent with those of Endalkachew et al. (2020); (Barut et al., 2023) and Rahman et al. (2023).

Figure 1. Correlation of different traits included.

Abbreviations are as presented under Table 3.

4. Conclusion

White cumin accessions showed highly significant variances for ten yield-related traits, essential oil and oleoresin contents. Seven accessions, namely, Shirka 001/2007, Sole-007, Akiya-2007, Bale-2007, Silingo-2007, Sagure-2007, and Gedgeda-026, were the high yielders and had analogous essential oil and oleoresin contents compared to Takusa-1 and Dembia-1 cultivars and could be advanced to over-location trials. Shirka-2007 and Shirka 001/2007 were prompt mature accessions. Those accessions could be used in future breeding programs, and research on the diversity among accessions needs to be undertaken. Multi-environment circumstances, molecular characterization, planting time assessment, and quality analysis of the accessions require more investigation.

Authors’ contributions

Gizaw Wegayehu drafted the manuscript, supervised the fieldwork, and conducted the analysis of variance, mean separation, and correlation. Kedir Jaleto and Awoke Ali coordinated fieldwork and collected data with the other co-authors. Nimona Fufa, Dasta Tsagaye, Demis Fikre, and Fekadu Gebretensay participated in the fieldwork, designing, and reviewing of the manuscript. The final manuscript was read and approved by each contributor.

Acknowledgments

The authors would express sincere gratitude for the financial support provided by the Ethiopian Institute of Agricultural Research to execute the study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that supports the findings of this study can be made available upon reasonable request.

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Gizaw Wegayehu Tilahun

Gizaw Wegayehu Tilahun has an M.Sc. in plant breeding and is a researcher at the Ethiopian Institute of Agricultural Research, Kulumsa Agricultural Research Center, Ethiopia. Moreover, he has published over three articles in reputed journals. His research interests include breeding for biotic and abiotic stress, molecular breeding, and participatory breeding.