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Department of Botany, Government institute of Science, Babasaheb Ambedkar Marathwada University Chhatrapati Sambhaji Nagar, Maharashtra, India
Onion (Allium cepa L.) is a globally important vegetable crop valued for its culinary, nutritional, and economic significance. However, onion productivity remains highly unstable, particularly during rainy (kharif) season cultivation, owing to excessive rainfall, high humidity, temperature fluctuations, and severe disease pressure. Genetic improvement through conventional breeding has been slow due to the crop?s biennial growth habit, cross-pollinated nature, high heterozygosity, and pronounced inbreeding depression. In this context, heterosis breeding has emerged as a powerful and reliable strategy for improving yield, quality, and environmental adaptability in onion. The discovery of cytoplasmic male sterility (CMS) by Jones and Clarke revolutionized onion breeding by enabling economical and large-scale hybrid seed production, circumventing the limitations imposed by floral morphology and manual emasculation. CMS-based hybrids have consistently exhibited substantial heterosis for bulb yield (30?60%), bulb size and uniformity, earliness, total soluble solids, storage life, and resistance to major diseases such as anthracnose (Colletotrichum spp) and usarium basal rot (Fusarium oxysporum f. sp. cepae). Genetic analyses using diallel and line ? tester mating designs have revealed the predominance of non-additive gene action for yield and several quality traits, further validating the suitability of heterosis breeding in onion. CMS-based hybrids are particularly advantageous under rainy season conditions, where they offer superior yield stability, enhanced disease tolerance, uniform maturity, and improved marketable quality compared with open-pollinated varieties. Although challenges such as limited CMS and restorer diversity, environmental sensitivity of sterility expression, and complexities in hybrid seed production persist, recent advances in doubled haploid technology, molecular characterization of CMS systems, and genomics-assisted breeding provide promising avenues for overcoming these constraints. This review critically synthesizes progress in CMS-based heterosis breeding in onion, with special emphasis on rainy season cultivation, and highlights future research priorities for developing climate-resilient, high-yielding, and quality-consistent onion hybrids.
Onion (Allium cepa L.) is one of the most widely cultivated vegetable crops globally and holds immense economic, nutritional, and culinary importance. It is an indispensable component of diets worldwide and contributes substantially to farm income, employment generation, and livelihood security in vegetable-based production systems (Anonymous, 2016; Griffiths et al., 2002; Brewster, 2008; Index Box, 2024). Owing to its year-round demand and wide adaptability, onion occupies a prominent position among vegetable crops in both developed and developing countries. India plays a vital role in global onion production, emerging as one of the leading producers and exporters in recent years. In 2022, onion was cultivated over approximately 1.9 million hectares in India, with a total production of about 31.27 million tonnes and an average productivity of 16.3 t ha?¹ (IndexBox, 2023). However, onion production during the agricultural year 2023–24 declined to 21.97 million tonnes, with Maharashtra (8.60 Mt), Madhya Pradesh (4.17 Mt), and Gujarat (2.06 Mt) being the major contributing states (Department of Agriculture and Farmers Welfare, 2024). Despite its leading position in global production surpassing even China in certain years, India's average productivity remains comparatively lower than that of several other major onion-producing countries. This yield gap highlights substantial scope for improvement through genetic enhancement, better agronomic management, and improved post-harvest infrastructure. Onion also holds considerable importance in India’s export economy, accounting for nearly 70% of the country’s total foreign exchange earnings from fresh vegetable exports (NHRDF, 2018). However, frequent fluctuations in production caused by climatic extremes, disease outbreaks, and post-harvest losses have led to volatility in domestic supply and international trade. Such instability often triggers sharp price fluctuations, affecting both farmers and consumers. Therefore, improving the productivity, quality, and stability of onion production is critical not only for food and nutritional security but also for sustaining export competitiveness and market stability. Among the different production seasons, rainy (kharif) season onion cultivation is particularly challenging and remains the most unstable. High rainfall, elevated humidity, and fluctuating temperatures during the monsoon period create highly favorable conditions for foliar diseases such as anthracnose (Colletotrichum spp) fusarium basal rot (fusarium oxysporum f. sp. cepae) and downy mildew (Peronospora destructor) leading to severe yield losses (Abubakar and Ado, 2008; Ambresh et al., 2013; Sharma, 2016). In addition, adverse weather conditions during the kharif season often result in bolting, delayed maturity, poor bulb development, and reduced storage life, collectively limiting marketable yield and profitability (Mahanthesh et al., 2008; NHRDF, 2018). Genetic improvement of onion through conventional breeding approaches has been inherently slow due to its biennial life cycle, high heterozygosity, and predominantly cross-pollinated breeding system (Jones and Davis, 1944; Veere Gowda, 1988). Early investigations clearly demonstrated that repeated selfing leads to severe inbreeding depression, manifested as reduced vigor, poor bulb formation, and low seed yield, whereas crossbreeding restores productivity through heterosis (Jones and Clarke, 1943; Jones and Davis, 1944). Subsequent studies consistently reported substantial heterosis for bulb yield, earliness, bulb size, uniformity, and quality traits such as total soluble solids and storage ability (Hosfield et al., 1977b; Joshi and Tanodom, 1976; Pal et al., 1988; Evoor et al., 2007). Heterosis breeding has therefore emerged as one of the most effective strategies for improving yield, quality, and adaptability in onion. Numerous studies have established that hybrid combinations consistently outperform their parental lines and open-pollinated varieties with respect to bulb yield, earliness, uniformity, and stress tolerance (Jones and Clarke, 1943; Hosfield et al., 1977b; Madalageri, 1983). However, the practical exploitation of heterosis in onion was historically constrained by the crop’s floral morphology, which makes manual emasculation technically difficult and economically unfeasible. The discovery of cytoplasmic male sterility (CMS) in onion by Jones and Clarke (1943) represented a major breakthrough, providing a practical and efficient mechanism for large-scale hybrid seed production. CMS-based hybrid breeding has since become the foundation of commercial onion improvement worldwide, enabling the development of genetically uniform, high-yielding hybrids with enhanced disease tolerance and environmental adaptability (Suciu and Tempelman, 1979; Havey, 1993; Jones et al., 2010; Singh et al., 2018). In recent years, CMS-based heterosis breeding has gained increasing relevance in tropical and subtropical regions, particularly for addressing the productivity and stability challenges associated with rainy season cultivation. Given the increasing demand for reliable onion production under monsoon conditions, CMS-based hybrid breeding offers a promising and sustainable strategy for improving yield stability, bulb quality, and disease tolerance during the kharif season. Against this background, the present review synthesizes current knowledge on onion botany, breeding behavior, male sterility systems, and heterosis breeding, with a specific focus on the role of CMS-based hybrids in enhancing rainy-season productivity. By critically analyzing existing research and identifying key breeding priorities and knowledge gaps, this review aims to provide a comprehensive framework to guide future onion improvement programs and strengthen the resilience of kharif onion production systems.
Contribution of Onion Seasons to Total Production in India.
Despite contributing a smaller share to total production, kharif and late kharif onions are crucial for maintaining market supply during the lean period between rabi harvests. However, productivity during the rainy season remains low due to excess moisture, disease incidence, and lack of well-adapted hybrids, emphasizing the need for targeted breeding interventions.
Figure 1. Relative contribution of rabi, kharif, and late kharif onion seasons to total onion production in India.
Ganesh Karad, Sunil Sangle*, Cytoplasmic Male Sterility?Based Heterosis Breeding for Yield and Quality Improvement in Onion (Allium cepa L.) with Special Reference to Rainy Season Cultivation, Int. J. Sci. R. Tech., 2026, 3 (3), 49-64. https://doi.org/10.5281/zenodo.18880810
10.5281/zenodo.18880810