K. N. Rai

Pathogenic Variation in the Pearl Millet Blast Pathogen Magnaporthe grisea and Identification of Resistance to Diverse Pathotypes

Blast, also known as leaf spot, caused by Pyricularia grisea (teleomorph: Magnaporthe grisea), has emerged as a serious disease affecting both forage and grain production in pearl millet in India. Pathogenic variation was studied in a greenhouse using 25 M. grisea isolates collected from four major pearl-millet-growing states in India (Rajasthan, Haryana, Maharashtra, and Uttar Pradesh) on 10 pearl millet genotypes (ICMB 02444, ICMB 02777, ICMB 06444, ICMB 93333, ICMB 96666, ICMB 97222, ICMB 99444, 863B, ICMR 06222, and ICMB 95444). Differential reactions to the test isolates were recorded on ICMB 02444, ICMB 93333, ICMB 97222, 863B, and ICMR 06222. The 25 isolates were grouped into five different pathotypes based on their reaction types (virulent = score ≥ 4 and avirulent = score ≤ 3 on a 1-to-9 scale). For the identification of resistance sources, a pearl millet mini-core comprising 238 accessions was evaluated under greenhouse conditions against five M. grisea isolates (Pg118, Pg119, Pg56, Pg53, and Pg45) representing the five pathotypes. Of 238 accessions, 32 were found to be resistant to at least one pathotype. Resistance to multiple pathotypes (two or more) was recorded in several accessions, while three accessions (IP 7846, IP 11036, and IP 21187) exhibited resistance to four of the five pathotypes. Four early-flowering (≤50 days) blast-resistant mini-core accessions (IP 7846, IP 4291, IP 15256, and IP 22449) and four accessions (IP 5964, IP 11010, IP 13636, and IP 20577) having high scores (≥7) for grain and green fodder yield potential and overall plant aspect were found to be promising for utilization in pearl millet improvement programs. Identification of five pathotypes of M. grisea and sources of resistance to these pathotypes will provide a foundation for breeding for blast resistance in pearl millet in India.

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 diversification 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 difference 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 efficiency will be the greatest with the A5 CMS system, followed by the A4 CMS system, and least with the currently commercial A1 CMS system.

Commercial viability of alternative cytoplasmic-nuclear male-sterility systems in pearl millet

Commercial viability of three cytoplasmic-nuclear male sterility (CMS) systems (A4, A5 and Av) as potential alternatives to the most widely used A1 system in pearl millet (Pennisetum glaucum (L.) R.Br.) was evaluated in terms of stability of complete male sterility of four isonuclear A-lines (81A1, 81A4, 81A5 and 81Av) and the level and stability of male fertility restoration of their 44 single-cross hybrids. Lines 81A4 and 81A5 had no pollen shedders (PS), and there were very low frequency of non-PS plants of these A-lines that had a maximum of 1–5% selfed seedset (SSS). In 81A1 and 81Av,there were, albeit low frequency (<1%) of PS plants, and relatively higher frequency of the non-PS plants in these two lines, the more so in 81Av,had 1–5% and even greater SSS. Some hybrids made on each of the three A-lines (81A1, 81A4 and 81Av) had high and stable male fertility, while others made on the same three A-lines displayed large variation in SSS across the environments, the more so in case of hybrids made on 81Av. These results indicate that the A4 CMS system provides a better alternative to the A1 CMS system, while the Av system does not. On the basis of highly stable male sterility and the highest frequency of pollinators behaving as maintainers, the A5 CMS system appeared to be the best for A-line breeding. The commercial viability of this CMS system in breeding R-lines of grain hybrids, however, still remains to be ascertained as no hybrid on it was fully male fertile in any environment.

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.

Ergot reaction of pearl millet hybrids affected by fertility restoration and genetic resistance of parental lines

SummaryPearl millet (Pennisetum glaucum (L.) R. Br.) hybrids based on the A1 cytoplasmic-nuclear male-sterile (CMS) lines are more susceptible to smut (Tolyposporium penicillariae Bref.) than open-pollinated varieties. Seventy eight pairs of hybrids, made onto male-sterile (A) lines and their counterpart maintainer (B) lines, were evaluated to examine the effects of male sterility and genetic resistance of parental lines on the smut severity of hybrids. The A-line hybrids had higher smut severity and lower selfed seedset than the counterpart B-line hybrids, indicating that it is the CMS-mediated male sterility rather than the A1 cytoplasm per se that caused greater smut severity of A-line hybrids. However, with the use of resistant parental lines even male-sterile hybrids of A-lines, in several cases, were as resistant as some of the highly resistant male-fertile hybrids of B-lines. It would be possible to produce smut resistant hybrids (< 10% severity) on A-lines, albeit in low frequency, even if only one parent of a hybrid were resistant. However, the probability of producing such hybrids would be higher when both parents were resistant to smut. Thus, improvement in smut resistance of parental lines and fertility restoration ability of pollinators would provide the most effective genetic approach to smut disease management in hybrids.

Effect of d2 dwarfing gene on grain yield and yield components in pearl millet near-isogenic lines

SummaryA d2 dwarfing gene in pearl millet [Pennisetum glaucum (L.) R. Br.] is currently being extensively used for the development of hybrid parents. Its effect on grain yield and yield components is poorly understood. Twelve pairs of tall and dwarf near-isogenic lines developed in the diverse genetic background of three composites were evaluated for grain yield and yield components for 2 years at two locations in southern India. The d2 gene or the genes linked to it, on an average, reduced plant height by 42%, grain yield by 14%, and head girth by 8% but increased head length and number of tillers per plant by about 5–6%. Large variations were observed among pairs (genetic background) for the difference between tall and dwarf near-isogenic lines for all of the above yield components resulting in no significant difference in five pairs and 17–35% less yield in dwarfs as compared to their tall counterparts in six pairs. Days to 50% flowering and seed weight were least affected by the d2 gene with the average difference between tall and dwarf groups of near-isogenic lines being of the order of 1–2%. These results indicate that the advantageous effects of d2 dwarfing gene can be effectively exploited by manipulating the genetic background. The difference between the average grain yields of tall and dwarf groups of near-isogenic lines showed considerable variation across environments with the dwarfs yielding as much as tall group in one environment and up to 30% less than the tall group in the other, thus, indicating that the d2 gene effect may be substantially modified by the environments.

Genetic architecture of open-pollinated varieties of pearl millet for grain iron and zinc densities

Genetic architecture of two commercial open-pollinated varieties of pearl millet (ICTP 8203 and ICMV 221) for grain iron and zinc densities was studied using 160 full-sib progenies each that were developed following North Carolina Design -1 and evaluated for two seasons. Results showed predominantly additive genetic variance and nonsignificant additive gene effect × environment interaction variance compared to large and significant dominance × environment interaction variance for both micronutrients in both populations. This translated into high narrow-sense heritability for Fe (65%) and Zn (86%) in ICTP 8203, and moderate heritability of 45% for both micronutrients in ICMV 221. In comparison, 1000-seed weight, generally assumed to be highly heritable, was predominantly under dominance gene control and had large dominance × environment interaction, giving the narrow-sense heritability estimates of 31% in ICTP 8203 and 13% in ICMV 221. These results, and highly significant and positive correlation observed between Fe and Zn densities, and non-significant correlations of these micronutrients with grain weight suggest that simultaneous selection for Fe and Zn densities in these populations can be effectively made without compromising the grain size.

Comparative Evaluation of Ground and Unground Pearl Millet and Sorghum Grain Samples for Determining Total Iron and Zinc

Rapid and effective methods are needed to analyze large numbers of grain samples for iron (Fe) and zinc (Zn) to select cultivars that are denser in these minerals. This study was conducted for the comparative evaluation of ground and unground grain samples for determining total Fe and Zn in pearl millet and sorghum cultivars with a range in seed size. In general, the results of the study with 50 pearl millet and 49 sorghum cultivars showed that grain Fe and Zn, in these relatively small-seeded crops, can be routinely determined using unground samples. Highly significant positive correlations were found between the values of Fe and Zn in grains of these crops determined using ground and ground samples.

Evaluation data of Pearl millet Initial hybrids for grain Iron, Zinc and agronomic traits during 2012 rainy season at Dhule( Maharashtra)

The experimental materials included in this study consisted of 31 hybrids. Trial was evaluated at collaborators location at Dhule (Mahatma Phule Krishi Vidhyapeeth) in randomized complete block design with three replications in 2012 rainy season. The plot size was two rows of 4 m length spaced at 50 cm apart, with plant-to-plant spacing of 15 cm within the rows at all the locations. All the recommended agronomic practices were followed for good crop stand. Days to 50% flower, grain yield and effective tillers per plant were recorded on plot basis. Five random plants were used to determine plant height and panicle length, and random samples of 200 grains were used to estimate 1000-grain weight. Grain samples were collected from open-pollinated panicles harvested at physiological maturity, sundried for more than 15 days and carefully threshed to ensure no dust contamination. These were analyzed for grain Fe and Zn content using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) at the Charles Renard Analytical Laboratory, ICRISAT, Patancheru, following the closed-tube method as described by Wheal et al. (2011). Experiment location on Google Map

Evaluation data of Pearl millet initial hybrids for grain Iron, Zinc and agronomic traits at Aurangabad during 2012 rainy season

The experimental materials included in this study consisted of 31 hybrids. Trial was evaluated at collaborators location at Aurangabad (Pioneer Hi-Bred Private Ltd.) in randomized complete block design with three replications in 2012 rainy season. The plot size was two rows of 4 m length spaced at 50 cm apart, with plant-to-plant spacing of 15 cm within the rows at all the locations. All the recommended agronomic practices were followed for good crop stand. Days to 50% flower, grain yield and effective tillers per plant were recorded on plot basis. Five random plants were used to determine plant height and panicle length, and random samples of 200 grains were used to estimate 1000-grain weight. Grain samples were collected from open-pollinated panicles harvested at physiological maturity, sundried for more than 15 days and carefully threshed to ensure no dust contamination. These were analyzed for grain Fe and Zn content using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) at the Charles Renard Analytical Laboratory, ICRISAT, Patancheru, following the closed-tube method as described by Wheal et al. (2011). Experiment location on Google Map