Performance evaluation of Kharif onion (Allium cepa L.) genotypes for morphological and yield traits

Introduction

Onion (Allium cepa L.) is one of the most widely cultivated vegetable crops worldwide owing to its culinary versatility, nutritional value and economic importance. A member of the family Amaryllidaceae, onion possesses a diploid chromosome number of 2n = 2x = 16. In India, it constitutes an important vegetable crop, serving both as a staple dietary ingredient and a major export commodity. Besides being a rich source of carbohydrates, proteins, dietary fibre, vitamins and essential minerals, onion contains bioactive phytochemicals, particularly quercetin and sulphur-containing lachrymatory compounds, which exhibit antioxidant, antiinflammatory, hypocholesterolemic and anticancer properties [1] . Onion production in India is highly seasonal, leading to pronounced fluctuations in market supply and prices. Onion prices generally remain high during September-November and decline from January to March-April. Since onion storage largely dependent on rabi bulbs, which are generally exhausted by August -September, storage losses often exceed 30%, leading to reduced market availability [2] and [3] . Consequently, kharif and late kharif onion cultivation plays a crucial role in maintaining onion availability during this period while providing farmers with better market prices than the rabi crop [3] . Despite its economic importance, kharif onion cultivation remains challenging because the crop is exposed to erratic monsoon rainfall, prolonged cloudy weather and continuous drizzling during crop growth. These conditions favour the development of foliar and soil borne diseases, increase weed infestation and adversely affect bulb yield and keeping quality. Consequently, kharif onion cultivation is confined to limited areas with relatively low productivity [4] These production constraints highlight the need for the development of genotypes better adapted to International Journal of Advanced Biochemistry Research 2026; SP-10(7): 564-568 kharif growing conditions. Therefore, the development of improved cultivars adapted to monsoon conditions is essential for sustaining kharif onion production. The development of improved cultivars adapted to kharif conditions depends largely on the availability and effective utilization of genetic variability. Knowledge of genetic variability and the association among economically important traits forms the basis of any crop improvement programme and facilitates the selection of superior genotypes. Therefore, characterization of available germplasm for qualitative and quantitative traits, together with the assessment of relationships among important traits is essential for the effective utilization of existing variability in onion breeding [5] . Most studies on onion diversity in India have primarily focused on a limited number of commercial varieties or local germplasm, resulting in inadequate exploration of the broader genetic diversity available within the crop. Comprehensive characterization of genetically diverse onion germplasm is essential for identifying promising parental lines for hybridization and future breeding programmes [6] . Consequently, the available genetic diversity remains underutilized, limiting the identification of diverse and promising parental lines. Morphological characterization serves as the first step in the description and classification of plant genetic resources and provides a reliable basis for assessing phenotypic diversity and identifying superior genotypes for crop improvement [7] . Therefore, the present study was undertaken to characterize 29 onion genotypes along with two commercially cultivated kharif onion varieties based on morphological and yield related traits under kharif conditions to identify superior genotypes for future onion breeding programmes.

Materials and Methods

A field experiment was conducted during the kharif season of 2023 at the ICAR-Directorate of Onion and Garlic Research (ICAR-DOGR), Rajgurunagar, Pune, Maharashtra, India (18.84° N, 73.88° E), situated in a subtropical dry humid agro-climatic region. The experiment was established in a Randomized Block Design (RBD) with three replications and comprised 29 onion genotypes along with two commercially cultivated kharif onion varieties. Fungicide-treated seeds were sown in the nursery during the second week of June 2023, and the crop was managed according to the recommended production practices of ICAR-DOGR for kharif onion. Data were recorded on key morphological and yield attributes, including plant height (cm), number of leaves per plant, pseudostem length (cm), pseudostem width (mm), equatorial diameter (cm), polar diameter (cm), neck thickness (mm), average bulb weight (g), yield per plot (kg plot⁻¹) and yield per hectare (t ha⁻¹).

Plant height was measured at harvest by recording the distance from the soil surface to the apex of five randomly selected plants from each plot using a steel scale. The mean plant height was calculated and expressed in centimetres (cm).

Number of leaves per plant

Five plants were randomly selected from each plot at harvest and the number of green, fully expanded functional leaves per plant was recorded. The mean number of leaves per plant was calculated for analysis.

Pseudo stem length (cm): Pseudo stem length was measured at harvest as the distance from the bulb top to the point of leaf base attachment using a steel scale. Measurements were recorded from five randomly selected plants in each plot and the mean pseudo stem length was expressed in centimetres (cm).

Pseudo stem width (mm): Pseudo stem width was determined at harvest using a vernier caliper by measuring the maximum diameter at the midpoint of the pseudo stem. Measurements were taken from five randomly selected plants in each plot and the mean value was expressed in millimetres (mm).

The equatorial diameter of the bulb was measured at its widest point (mid-length) using digital vernier calipers in millimeters (mm). These values were subsequently converted to centimeters (cm) to calculate the mean for each treatment.

Polar diameter (cm) was measured at harvest using a digital vernier caliper between the polar ends of five randomly selected bulbs from each plot. Measurements recorded in millimetres (mm) were converted to centimetres (cm) and the mean polar diameter was calculated.

Neck thickness (mm): Neck thickness was measured at the narrowest point of the neck above the bulb using a digital vernier caliper. Measurements were recorded from five randomly selected bulbs in each plot and the mean neck thickness was calculated.

Average bulb weight (g): Average bulb weight was determined at harvest by weighing five randomly selected bulbs from each plot using a digital weighing balance. The mean bulb weight was calculated and expressed in grams (g).

Yield per plot (kg) was recorded after field curing by weighing the total bulb yield harvested from each plot. Total yield comprised marketable bulbs as well as unmarketable bulbs, including split, doubled, rotted, and prematurely bolted bulbs, and was expressed as kilograms per plot (kg plot⁻¹).

Marketable bulb yield was estimated from the marketable bulbs harvested from each plot after field curing by excluding split, doubled, rotted, unmarketable, and prematurely bolted bulbs. The plot yield was converted to tonnes per hectare (t ha⁻¹).

Statistical analysis

The experimental data were subjected to analysis of variance (ANOVA) using a Randomized Block Design (RBD). Statistical analyses were performed using the R-based web application GRAPES version 1.1.0 [8] . Genotype means were separated using Tukey's Honest Significant Difference (HSD) test at the 5% probability level (P≤0.05).

Discussion

Plant height is primarily governed by the genetic constitution of the genotype, although its expression is also influenced by the prevailing kharif environmental conditions, including temperature, rainfall and soil fertility. Comparable observations have been reported by [9] and [3] . Leaf production depends on the vegetative growth potential of the genotype and its ability to initiate new leaves under prevailing environmental conditions. Under kharif conditions, factors such as frequent rainfall, high humidity, fluctuating temperatures and reduced sunshine may further influence leaf initiation and development. Similar observations were reported by [10] and [3] . Pseudostem length reflects the vegetative vigour of onion genotypes and is largely governed by their genetic potential. Similar observations were reported by [9] . Pseudostem width is an important indicator of vegetative growth and differed among the evaluated genotypes owing to their genetic constitution. Comparable observations were also reported by [11] . Equatorial diameter is a key determinant of bulb size and is influenced by genetic factors regulating bulb development.

Under kharif conditions, excessive rainfall and intermittent waterlogging may further restrict bulb enlargement by impairing root function and assimilate translocation [12] ; [13] and [14] . Similar observations have been reported by [15] and [16] . Polar diameter represents bulb growth along the longitudinal axis and is primarily influenced by the genetic potential of the genotype. Comparable findings were reported by [15] and [16] . Neck thickness is influenced by the maturity behaviour and genetic constitution of onion genotypes, while excessive nitrogen fertilization may promote the development of thicker necks [17] . Similar observations were documented by [17] and [9] . Average bulb weight reflects the efficiency of bulb development and assimilate accumulation among the evaluated genotypes. Comparable observations have been reported by [18 , 3] and [19] . Yield per plot reflected the productive potential of the evaluated genotypes under kharif conditions. Bulb yield per hectare represents the cumulative expression of yield contributing traits and the genetic potential of the evaluated genotypes. Similar findings were reported by [20 , 19] and [16] .

Conclusion

The present study demonstrated considerable variability among the evaluated onion genotypes for morphological and yield-related traits under kharif conditions, indicating substantial scope for selection of superior genotypes. Among the evaluated genotypes, DOGR-2118 emerged as the most promising owing to its superior bulb weight and yield performance, while RHRO-2022-10 exhibited excellent vegetative growth. The superior performance of these genotypes suggests their potential for cultivation under kharif conditions as well as their utilization in future onion breeding programmes. Overall, the findings provide valuable information for the selection of promising genotypes aimed at improving productivity and adaptation in rainy season onion.

Acknowledgement

The first author also gratefully acknowledges the Mahatma Jyotiba Phule Research Fellowship (MJPRF-2023), Government of Maharashtra (File No. MAHAJYOTI/Ph.D.Fellow2023/2821, dated 11 October 2024), for providing financial support during her Ph.D. programme.

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