Fertility restoration studies on diverse cytoplasm sources in Pearl millet [Pennisetum glaucum (L.) R. Br.]

Introduction

The presence of exploitable male sterility mechanisms in pearl millet has enabled the commercial utilization of heterosis and hybrid vigor to enhance productivity. The discovery of Tift 23A 1 , a cytoplasmic-nuclear male sterility (CMS) and its effective application in producing male sterile lines for commercial pearl millet hybrids production marks a significant milestone in the improvement of pearl millet (Athwal, 1965; Burton and Athwal, 1967 and Burton and Powell, 1968) [2,4,3] . In the 1970s, when hybrids based on the Tift 23A 1 cytoplasm faced susceptibility to downy mildew infection, research endeavors in pearl millet breeding centers were intensified. Their focus was on diversifying the genetic foundation of male sterile lines in the A 1 cytoplasmic system and investigating alternative CMS systems within pearl millet. Burton and Athwal (1967) [4] employed A 1 , A 2 and A 3 CMS sources for hybrid development while Marchais and Pernes (1985) [8] identified two other sources (A 1 and A 4 ) derived from distinct accessions of Pennisetum glaucum monodii, a wild relative of cultivated pearl millet. Additionally, a completely novel A 5 cytoplasmic male sterility system was created by Rai (1995) [9] . This development showcased the ongoing efforts to explore and enhance male sterility mechanisms within pearl millet for the purpose of breeding improved hybrids. Although various cytoplasmic male sterility systems exist within pearl millet, there is a notable scarcity of comprehensive research on the identification of restorers for these diverse cytoplasms. Among the extensively evaluated systems like A 2 and A 3 , none demonstrated superior performance compared to the A 1 CMS system in relation to one or more crucial pearl millet traits. While the A 4 and A 5 sources displayed high stability, their practicality is limited due to the absence of appropriate restorers (Rai et al., 2006) [10] . Therefore, it is imperative to focus on this aspect in order to effectively utilize the array of sterile sources in creating new pearl millet hybrids. Developing suitable restorers is vital for the continued advancement of commercial hybrid varieties.

The availability of cytoplasmic genetic male sterile lines in this crop facilitates the practical exploitation of heterosis for commercial purposes and the large scale production of hybrid seeds. The application of heterosis at a commercial level in pearl millet is considered a significant advancement in enhancing its productivity.

Materials and Methods

The material for the present study comprises of three female parents from diverse cytoplasmic male sterility sources (A 1 , A 4 and A 5 ) and 20 elite restorers. The three female parents viz., ICMA 98222 (A 1 cytoplasm), ICMA 04777 (A 4 cytoplasm) and ICMA 01777 (A 5 cytoplasm) and the 20 restorers viz., BRBL 1136R, ICMR 15455- [6] , so as to obtain sixty F 1 hybrids during summer 2022-23. Artificial selfing and crossing operations were carried out as suggested by Rao (1952). To ensure selfing, the panicles of the parents, just before the emergence of stigma were covered with butter paper bag. After complete protrusion of stigma, the panicle of the seed parent was dusted with pollen collected from the male parent and rebagged. Pollination was effective between 8.00 am to 11.00 am. The resultant hybrids along with their parents and checks were raised in Randomized Complete Block Design with three replications during Kharif 2023 at Regional Agricultural Research Station, Vijayapura. Each hybrid was accommodated in two rows of three meter row length in three replications with a row spacing of 45 cm and plant to plant spacing of 15 cm. Randomly selected five competent plants in each treatment (hybrid) were selfed with brown paper bags before flowering and same plants were used for recording the observations. At maturity stage, numbers of seeds were counted out of total number of spikelets per ear head and seed set percentage was calculated (Kishan and Borikar, 1989) [7] and classified the percentage seed set as given below.

Results and Discussion

The study evaluated the fertility restoration ability of twenty testers on three diverse CMS lines A 1 , A 4 and A 5 based sources during the Kharif 2023. The selfing study data illustrate the percentage of seed set in several cross combinations involving diverse cytoplasms. The outcomes displayed in Table 1 predicted that the values of the seed set ranged from 32 to more than 90 per cent. The compatibility of the cytoplasm of the female gamete or egg with the nuclear background of the male gamete is one factor that affects the seed set. Extreme variation in the different crosses may be caused by distinct interactions between the nuclear background of the male gamete and the female gamete in that particular line. Similar outcomes were obtained by Amiribehzadi and Satyavati (2012) [1] , Salagarkar et al. (2016) [11] , Singhal et al. (2019) [12] and Chandra et al. (2022) [5] . The fertility restorers that have been identified can be employed for the subsequent creation of new experimental hybrids in pearl millet breeding.

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