Pearl millet downy mildew research in India: progress and perspectives

Downy mildew (DM), caused by Sclerospora graminicola, continues to be a major biotic constraint to pearl millet [Pennisetum glaucum (L.) R. Br.] production in India. The disease which had remained incipient on local landrace cultivars until the 1960s, became a serious threat to high-yielding, single-cross hybrids introduced into cultivation during the late 1960s. The first epiphytotics of DM occurred during the crop season of 1971 on the first popular hybrid HB 3 and caused substantial yield loss (Nene and Singh 1976). With the establishment of ICRISAT in 1972, pathological research on pearl millet began in 1974 to address the major diseases: downy mildew, ergot (Claviceps fusiformis), smut (Moesziomyces penicillariae) and rust (Puccinia substriata var indica). A Consultative Group meeting on downy mildew and ergot was held in 1975 at ICRISAT-Patancheru to review the status of research and identify priorities. The group, consisting of renowned plant pathologists and plant breeders from India and other countries, made several recommendations for downy mildew research relating to the internal seedborne nature of the pathogen, its likely transmission and methods to eliminate the pathogen from the seed; the relative roles of oospores, sporangia and seedborne inoculum in epidemiology; development of screening techniques; existence of physiologic races; multilocation evaluation of resistant lines to identify stable resistance; and development of chemical and cultural methods to supplement the principal host-plant resistance method of disease control (ICRISAT 1975). These recommendations formed the basis for downy mildew research encompassing basic, strategic and applied aspects. These are still being followed in our ongoing Indian Council of Agricultural Research (ICAR)-ICRISAT partnership research

Panicle surface area as a selection criterion for grain yield in pearl millet (Pennisetum glaucum)

In an experiment 24 experimental varieties of 3 composites, viz 'EC 87', 'EC 91' and 'HHVBC', were evaluated during rainy season of 1996 and 1997 in 11 environment at 3 locations for the effect of selection for panicle surface area on grain yield and its components in pearl millet [Pennisetum glaucum (L.) R. Br. emend. Stuntz]. Singificant variation was observed among experimental varieties for all the traits, The actual gain in 'PCV 5' (with maximum panicle surface area) over the original population was 8.7% for grain yield/m across the composites. Breeder selection was effective in improving grains/m by an average of 4% in 3 composited, but it was effective in improving grain yield/m over the original population by 3% in 'EC 91; only. The net increase in grain yield/m was almost similar to the prediction (+8.7% vs prediction of 10%). Also the selection for large panicle surface area, ie 'PCV 5', was more effective than breeder selection for grain yield/m by an average of 9% in the 3 composites, The panicle surface area showed positive correlation with grain number/m, grain size and grain yield/m among experimental varieties (PCV 1' to PCV 5') in 3 population

Strategy for downy mildew resistance breeding in pearl millet in India

Downy mildew (DM) caused by Sclerospora graminicola is a widespread and economically most important disease of pearl millet causing substantial annual yield losses, particularly in single-cross F1 hybrids in India. Currently, in India about 50% of the 9 million ha under pearl millet cultivation is grown with more than 70 hybrids in which DM incidence has been highly variable, with some hybrids showing more than 90% incidence in farmers' fields. With increasing area under hybrid cultivation since the 1970s the disease has become more severe due to evolution of new virulent pathotypes in response to new hybrid genotypes. At ICRISAT, breeding for DM resistance using conventional pedigree breeding and more recently marker-assisted backcross breeding has been successful, and a large number of disease resistant hybrids have been developed and deployed. This has, to a large extent, helped in arresting the occurrence of widespread DM epidemics since the 1990s. In view of the increasing severity of the disease and evolution of new more virulent pathotypes, there is a need to develop a long-term DM resistance breeding strategy in India. In this paper, we discuss various aspects of the pearl millet-DM pathosystem, factors that influence disease resistance breeding and suggest short-, medium- and long-term strategies for DM resistance breeding

Establishment of a pearl millet [Pennisetum glaucum (L.) R.Br.] core collection based on geographical distribution and quantitative traits

ICRISAT conserves a large collection of pearl millet [Pennisetum glaucum L. R. (Br.)] comprising of 21,392 accessions. This includes landraces, cultivars, genetic stocks, breeding lines, and wild relatives from 50 countries. However, only a small fraction of this huge collection has been exhaustively used in the pearl millet improvement program. The objective of our research was to develop a core collection of pearl millet to enhance utilization of genetic resources in improvement programs and simplify their management. For this purpose, accessions were initially stratified according to geographical distribution followed by hierarchical clustering on 11 quantitative traits using Ward's method. This resulted in 25 distinct groups. Approximately 10% accessions were then randomly selected from each of these 25 distinct groups to form a core collection of 1,600 accessions. Different statistical methods like comparison of mean using Newman-Keuls test, variance using Levene's test, frequency distributions using Chi-square test, and Wilcoxon's rank-sum non-parametric test for the traits validated that the variation present in entire collection had been preserved in the core collection. The important phenotypic correlations among different traits that may be under the control of co-adapted gene complexes were also preserved in the core collection. The diversity represented in the core collection will therefore, be a guideline to breeders for a wider use of the pearl millet genetic resources available in the genebank

Yield Gap Analysis of Sorghum and Pearl Millet in India Using Simulation Modeling:Global Theme on Agroecosystems Report no. 37

Sorghum and pearl millet are the staple cereals and important source of fodder for animals in the semi-arid and arid parts of India. In the present study, we have: a) characterized the distribution of sorghum and pearl millet in different production zones in India; b) estimated their rainfed potential, achievable and current levels of farmers’ yields; c) quantified the gaps between farmers’ yields and rainfed potential yields; and d) suggested ways to abridge the yield gaps. Using CERES-sorghum and CERES-pearl millet crop growth models and historical weather data, rainfed potential yields and water balance of sorghum (kharif and rabi) and pearl millet were estimated for selected locations in different production zones. Simulated yields were supplemented with the research station yields of rainfed trials and yields of frontline demonstrations, both obtained from the reports of the All India Coordinated Crop Improvement Projects on Sorghum and Pearl Millet. District level yields were considered as farmers’ yields. Based on these data, the yield gaps at various management levels were estimated. The farmers’ average yield was 970 kg ha-1 for kharif sorghum, 590 kg ha-1 for rabi sorghum and 990 kg ha-1 for pearl millet. Simulated rainfed potential yield in different production zones ranged from 3210 to 3410 kg ha-1 for kharif sorghum, 1000 to 1360 kg ha-1 for rabi sorghum and 1430 to 2090 kg ha-1 for pearl millet. Total yield gap (simulated rainfed potential yield - farmers’ yield) in production zones ranged from 2130 to 2560 kg ha-1 for kharif sorghum, 280 to 830 kg ha-1 for rabi sorghum and 680 to 1040 kg ha-1 for pearl millet. This indicates that productivity of kharif sorghum can be increased 3.0 to 4.0 times, rabi sorghum 1.4 to 2.7 times and pearl millet 1.8 to 2.3 times from their current levels of productivity. To abridge the yield gaps of sorghum and pearl millet, integrated watershed-based approach encompassing harvesting of excess rainfall for supplemental irrigation, growing high yielding crop cultivars, integrated nutrient management and integrated pest and disease management would be required. Value addition of products and their multiple uses are necessary to make them more remunerative for the farmers

Influence of cytoplasmic-nuclear male sterility systems on microsporogenesis in pearl millet (Pennisetum glaucum (L.) R. Br.)

Influence of a range of cytoplasms on microsporogenesis and anther development in pearl millet was studied using six isonuclear A-lines having five cytoplasms (A1, A2, A3, A4 and Av) and the nuclear genome of 81B. 81B was used as a male-fertile control. Microsporogenesis and anther development were normal in 81B. However, pollen mother cell (PMC)/microspore/pollen degeneration in the six A-lines occurred at different stages of anther development. Each cytoplasm had its unique influence on microsporogenesis and anther development as evidenced by different developmental paths followed by them leading to pollen abortion. The cause of pollen abortion differed from line to line, from floret to floret within a spikelet, from anther to anther within a floret, and in some cases even from locule to locule within an anther. Events that led to male sterility included anomalies in tapetum and callose behaviour, persistence of tapetum, endothecium thickness, and other unknown causes. The present study also indicated that anther/pollen development was more irregular in Pb 406A3. In 81A4 and 81A1 > 95% of anther locules followed a definite developmental path to pollen abortion. In the other A-lines many developmental paths were observed within the line and pollen degeneration occurred at various stages. This could be one of the reasons for greater instability of male sterility in the A2 and A3 systems and greater stability of male sterility in the A1 and A4 systems

Seed parent breeding efficiency of three diverse cytoplasmic-nuclear male-sterility systems in pearl millet

Pearl millet (Pennisetum glaucum (L.) R. Br.) hybrids, grown widely in India and to some extent in the US, are all based on an A1 CMS source, leaving the pearl millet hybrids vulnerable to potential disease or insect pest epidemics. A comparison of this CMS system with two additional CMS systems (A4 and A5) in the present study based on isonuclear A-lines (seed parents) and their isonuclear hybrids showed that A-lines with the A4 cytoplasm had much fewer pollen shedders and much reduced selfed seed set in visually assessed non-shedding plants as compared to those with the A1 cytoplasm. A-lines with the A5 cytoplasm had neither any pollen shedders nor did they set any seed when selfed. This showed that the A5 CMS system imparts complete and most stable male sterility, followed by the A4 and A1 CMS systems. The frequency of maintainers, averaged across a diverse range of 26 populations, was highest for the A5 CMS system (98%), followed by the A4 (59%) and the A1 (34%) system indicating the greatest prospects for genetic diversiWcation of A-lines lies with the A5 cytoplasm, and the least with the A1 cytoplasm. Mean grain yield of hybrids with the A1 cytoplasm was 5% more than the A4-system hybrids, while there was no diVerence between the mean grain yield of hybrids based on A1 and A5 CMS systems. Based on these results, it is suggested that seed parents breeding eYciency will be the greatest with the A5 CMS system, followed by the A4 CMS system, and least with the currently commercial A1 CMS system

Effect of pollen and DNA source on RFLP pattern of mitochondrial DNA in pearl millet

In this study, RFLP banding patterns based on mitochondrial DNA (mtDNA) for the open-pollinated (OP) seed were identical to those based on mtDNA from sibbed seed of pearl millet. This clearly indicated that OP and sibbed seed can be used for mtDNA-RFLP analysis with equal reliability. In all four enzyme-probe combinations tested, RFLP banding patterns were identical from total DNA (tDNA) and mtDNA Southern blots. The only difference observed was that bands appeared hazy and their resolution was reduced when tDNA was used. A few bands with very similar molecular weights appeared fused, resulting in thick hazy bands when digested tDNA was used in place of digested mtDNA

Assessment of genetic diversity within and between pearl millet landraces

A minimum core subset of pearl millet (Pennisetum glaucum), which comprised 504 landrace accessions, was recently established from the global pearl millet germplasm collection of ICRISAT. The accessions for this core were selected by a random proportional sampling strategy following stratification of the entire landrace collection (~16?000 accessions) according to their geographic origin and morpho-agronomic traits. In this study, RFLP probes were used to quantify the genetic diversity within and between landrace accessions of this minimum core using a subset comprising ten accessions of Indian origin. Twenty-five plants per accession were assayed with EcoRI, EcoRV, HindIII and DraI restriction enzymes, and 16 highly polymorphic RFLP probes, nine associated with a quantitative trait loci (QTLs) for downy mildew resistance, and five associated with a QTL for drought tolerance. A total of 51 alleles were detected using 16 different probe-enzyme combinations. The partitioning of variance components based on the analysis of molecular variance (AMOVA) for diversity analysis revealed high within-accession variability (30.9%), but the variability between accessions was significantly higher (69.1%) than that within the accessions. A dendrogram based on the dissimilarity matrix obtained using Ward's algorithm further delineated the 250 plants into ten major clusters, each comprised of plants from a single accession (with the exception of two single plants). A similar result was found in an earlier study using morpho-agronomic traits and geographic origin. This study demonstrated the utility of RFLP markers in detecting polymorphism and estimating genetic diversity in a highly cross-pollinated species such as pearl millet. When less-tedious marker systems are available, this method could be further extended to assess the genetic diversity between and within the remaining accessions in the pearl millet core subset

Pearl Millet Crop Management and Seed Production Manual

Pearl millet is a major warm season coarse grain cereal grown on 26 million ha in some of the harshest semi-arid tropical environments of Asia and Africa. India has the largest area (9–10 million ha) under this crop, ranking it third along with sorghum. It is cultivated in the most sandy, infertile soils and droughty environments (eg, arid Rajasthan) where no other cereal crop can survive. Even under these conditions, pearl millet yields 300–400 kg ha-1 of grain. Pearl millet hybrids maturing in 80–85 days, when cultivated as an irrigated summer season crop in parts of Rajasthan, Gujarat and Uttar Pradesh states of India, have been reported to give as high as 4000–5000 kg ha-1 of grain yield. Pearl millet grains have high protein content, balanced amino acid profile, and high levels of iron, zinc, and insoluble dietary fiber. Eggs produced from layers fed on a diet of pearl millet have much lower levels of LDL (the bad cholesterol) than those fed on a maize-based diet. These adaptive and nutritional features combined with high yield potential make pearl millet an important cereal crop that can effectively address the emerging challenges of global warming, water shortages, land degradation and food-related health issues. Farmers cultivating pearl millet continue to be plagued by uncertain and low economic returns when production falls and also when production increases (due to low prices). This serves as a deterrent for farmers to invest in improved crop management, although the latter can play an effective dual role in increasing productivity and enhancing production stability. The demand for pearl millet grain is likely to increase with its increasing use as poultry and animal feed. This demand can further increase if pearl millet enters the commercial convenience foods channel, thereby increasing grain price. In turn, this will lead to greater investment in crop management and consequently productivity enhancement. The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and National Agricultural Research System (NARS) in India have played a pioneering role in developing a diverse range of improved breeding lines and parental lines of potential hybrids. These lines have been used extensively by breeding programs in both the public and private sectors to develop and commercialize a large number of hybrids (more than 70 were under cultivation in 2006). These hybrids are cultivated on 50% of the total pearl millet area, leading to 65% increase in grain yield during the past 20 years. Since its inception in 1974, the All India Coordinated Pearl Millet Improvement Project (AICPMIP) has developed production-protection technologies specific to agro-ecoregions of different states. Their application holds the promise of further enhancing the productivity of improved cultivars to commercial farming scales, and hence increasing the profitability of their cultivation, similar to the one witnessed in the seed production sector. This lucid and comprehensive manual on pearl millet crop management and seed production by AICPMIP and ICRISAT scientists delves into pearl millet biology, its distribution and climatic requirements; and various aspects of crop management and seed production. Though written primarily in the context of agriculture in India, its contents have a wider application for students, teaching and training personnel, extension workers and farmers interested in development, crop management and seed production and marketing of pearl millet