Hybridization and identification of resistant sources for major diseases in pearl millet (Pennisetum glaucum (L.) R. Br)

Introduction

Pearl millet is a diploid (2n = 2x = 14) in nature stands out as an exceptionally drought resistant, warm season millet crop that primarily serves as a staple food source for millions of the people in the world and provides fodder for animals and poultry feed. It's nutritionally excellence and fundamental role in the sustenance of numerous populations residing in challenging environments characterized by unpredictable rainfall patterns and impoverished soils. It is the most suitable and efficient choice crop for arid and semiarid conditions due to its exceptional ability to make efficient use of soil moisture and its higher tolerance to heat in comparison to sorghum and maize. It also possesses unique genetic predisposition to withstand environmental stress and produce appreciable yield when cultivated on marginal soils. Its cultivation typically takes place in soil marked by diminished fertility receiving an annual rainfall ranging from 150 to 750 mm. The year 2023 has been declared as the "International Year of Millets" by the FAO, Committee on Agriculture (COAG) forum. Micronutrient malnutrition is increasingly being recognised as a serious public health problem affecting more than half of the population worldwide, with preschool children and women in developing countries being the most vulnerable (Anon., 2004). Improving essential nutrient content in staple food crops through biofortification breeding can overcome the micronutrient malnutrition problem. The most widespread of these are dietary deficiencies in iron (Fe), zinc (Zn) and vitamin A. Iron deficiency is the principal cause of anemia, this impairs children physical growth and mental development, while due to Zn deficiency children have stunted growth. Pharmaceutical supplementations, industrial food fortification, agricultural approaches to dietary diversification and biofortification have been suggested to address these problems. The crop production and productivity is adversely affected by a number of abiotic stresses (drought and heat) and biotic stresses such as diseases (downy mildew [Sclerospora graminicola], blast [Pyricularia grisea; teleomorph: Magnaporthe grisea], rust [Puccinia substriata var. indica], ergot [Claviceps fusiformis] and smut [Moesziomyces penicillariae]). Breeding for downy mildew resistance has always been the top priority in the pearl millet breeding programs in India owing to economic importance of the disease (Rai et al. 2014) [8] . However, during recent years, blast, also known as leaf spot, has gained equal importance due to its widespread occurrence in India. In fact, the disease has attained an alarming status requiring concerted efforts to breed for resistance to blast (Sharma et al. 2018) [9] . Rust, a foliar disease reduces seed yield in hybrid seed production plots and adversely affects biomass and quality of forage and grain yields in pearl millet cultivars. Use of host plant resistance is the most feasible and economical means of managing these diseases as the crop is mainly cultivated by resource-poor farmers. Hence, in present investigation an attempt was made to identify blast and rust resistant potential hybrids.

Materials and Methods

A total of 50 hybrids, 27 parents and three checks were screened for blast and rust disease reaction during kharif 2023 at Regional Agricultural Research Station, Vijayapura. Each entry was planted in two rows of 3 m length with a spacing of 45 cm × 15 cm. During the complete crop period, standard package of practices of Zone 3 of Karnataka were followed.

Observations on disease incidence

The blast and rust disease severity was recorded at the time of maturity using 0-9 scale as per the method suggested by Mayee and Datar (1986) [5] by randomly selecting five plants in each genotype. In each entry, severity was recorded by considering lower leaves, middle leaves and top leaves of pearl millet genotypes at maturity stages and based on the disease reaction, genotypes were categorized into immune, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible as mentioned below. Typical rust pustules covering 26 to 50 per cent of the leaf area Susceptible (S) 9

Rust pustules covering 51 per cent or more of the leaf area and withering of leaf Highly susceptible (HS)

Scale for scoring pearl millet blast disease severity

Genotypes and checks were later grouped into different categories based on their reaction to blast and rust disease under unprotected conditions.

Results and Discussion

The degree of disease severity in parents, hybrids and checks regarding blast reaction was recorded using a Scale ranging from 0 to 9 at the crop maturity stage (Mayee and Datar, 1986) [5] .

The data in present study revealed that out of the 80 genotypes analyzed, not a single one registered immunity. Among these, 21 genotypes (comprising 6 testers, 14 hybrids and 1 check) exhibited resistance to blast, while 50 genotypes (including 2 lines, 15 testers, 31 hybrids and 2 checks) displayed a moderate level of resistance. In contrast, 9 genotypes (4 testers and 5 hybrids) demonstrated a moderate susceptible reaction. None of the genotypes were categorized as susceptible and highly susceptible to blast (Table 1).

In the past, researchers from both India and other countries have made efforts to identify the factors behind resistance to the pearl millet blast pathogen. Comparable outcomes were documented in studies conducted by Sharma et al. (2009) [11] , Nagaraja (2013) [6] , Lubadde (2014) [4] , Sharma et al. (2020) [10] , Athoni et al. (2022) [2] , Parihar et al. (2022) [7] and Kumara et al., 2023 [3] . Using a 0-9 scale, the disease severity in the parents, hybrids and checks for rust reaction were recorded at the maturity stage (Mayee and Datar, 1986) [5] . Out of the eighty genotypes that were evaluated, the data showed that none were found immune. Nineteen genotypes including 2 lines,6 testers and 11 hybrids showed resistant reaction for rust and fifty three genotypes (including 16 testers, 34 hybrids and 3 checks) were reflected to be moderately resistance. A fairly susceptible reaction was shown by 8 genotypes (3 testers and 5 hybrids). Additionally, none of the genotypes was discovered to be either vulnerable or very susceptible to rust disease (Table 2).

In the past, several researchers from India and across the world have tried to identify the reasons behind resistance to the pathogen that causes pearl millet rust. Nagaraja (2013) [6] , Lubadde (2014) [4] , Sharma et al. (2020) [10] , Athoni et al. (2022) [2] and Kumara et al. 2023 [3] noted similar outcomes from thesis study. ) with varying degrees of resistance to moderately resistant reaction for rust and blast in comparison to checks (Table 4).

References

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