P. Sanjana Reddy

Combining ability and heterosis as influenced by male-sterility inducing cytoplasms in sorghum [Sorghum bicolor (L.) Moench]

An investigation was carried out to assess the efficiency of A2 cytoplasmic-nuclear male-sterility (CMS) system in comparison to the widely used A1 cytoplasm in terms of general combining ability (gca) effects of male-sterile (A-) lines and mean performance, specific combining ability (sca) effects and mid-parent heterosis of hybrids for days to 50% flowering, plant height and grain yield at International Crops Research Institute for the Semi-Arid Tropics, Patancheru, Andhra Pradesh, India in 2001 and 2002 rainy seasons. The material for the study consisted of six pairs of iso-nuclear, allo-plasmic (A1 and A2) A-lines and 36 iso-nuclear hybrids produced by crossing these A-lines with three dual restorer (R-) lines. The results revealed that cytoplasm and its first-order interaction with year, R- and A-lines did not appear to contribute to variation in iso-nuclear hybrids for plant height and grain yield. Cytoplasm had limited effect on gca effects of A-lines and on sca effects and mid-parent heterosis of iso-nuclear hybrids for days to 50% flowering, plant height and grain yield. The mean days to 50% flowering, plant height and grain yield of A2 cytoplasm-based hybrids were comparable with those of widely used A1 cytoplasm-based hybrids. The relative frequency of the occurrence of the A1- and A2-based hybrids with significant sca effects and mid-parent heterosis indicated that A2 CMS system is as efficient as A1 with a slight edge over A1 for commercial exploitation. The implications of these results are discussed in relation to opportunities for broadening not only cytoplasm base but also nuclear genetic base of both the hybrid parents.

History of post-rainy season sorghum research in India and strategies for breaking the yield plateau

Post-rainy (rabi) sorghum grows under residual soil moisture conditions and is important for food and fodder security especially during dry seasons in semi-arid regions of India. Unlike rainy sorghum being dominated with hybrids, post-rainy sorghum growing areas are cultivated with varieties especially landrace selections. Much of the area is covered by M 35-1, a landrace selection developed seven and half decades ago. Post-rainy sorghum research did not receive much emphasis until nineties and the varieties or hybrids bred and released could not match M 35-1 in yield or quality. Some progress has been made recently with the release of varieties for specific soil depths viz., shallow, medium and deep soils. Efforts made to develop hybrids with wider adaptability to varied production environments did not fetch much success. The hybrids lacked significant heterosis, grain quality and shoot fly resistance comparable to M 35-1. Also, low temperatures at anthesis caused poor seed settings in hybrids. Strategic research is required to develop new varieties and hybrids for post-rainy season to break the yield plateau.

Phenotyping in Sorghum [Sorghum bicolor (L.) Moench]

Sorghum is one of the most important cereal crops grown in the semi-arid tropics (SAT) of Asia, Africa and Americas for its food, feed, fodder and fuel value. Sorghum production is constrained by several biotic and abiotic stresses. Genetic enhancement of sorghum for grain and stover yield, nutritional quality and plant defense traits (abiotic and biotic) which stabilize the crop performance requires thorough knowledge on crop genetic and crop breeding principles. Rapid progress in biotechnology provided powerful and cost-effective molecular/genomic tools to develop desired products in sorghum. However, development of robust and efficient phenotyping methods for traits of interest is critical to make use of these new tools. There is no publication with efficient phenotyping protocols for sorghum research compiled at one place for use by sorghum workers. This book chapter is an attempt to fill that gap and we hope various phenotyping methods discussed hereunder will be useful to sorghum researchers in developing improved products by using them in combination with appropriate breeding/genomic tools.

Can Cold Tolerance Bring in Hybrids on Commercial Front in Winter Sorghum

Studies on early-season and mid-season cold temperature stress on growth and yield components in diverse classes of winter sorghum are essential for targeting hybrid development that is otherwise confined only to rainy season-grown sorghum. The results showed that from among the 194 winter sorghum genotypes belonging to 5 groups - varieties, B-lines, R-lines, hybrids and germplasm lines, 81% of the genotypes were correctly placed in their respective groups based on discriminant analysis. Principal component analysis showed that most of the traits involved in the study are important and variability cannot be explained by a few traits and the traits recorded at seedling and maturity stages were explained by different principal components. Most of the traits recorded under cold stress at seedling stage did not correlate with those recorded under cold stress at anthesis. There is scope for improvement of individual groups for seedling dry fodder yield and grain yield, more so in the case of hybrids and female parental lines. Breeding for cold tolerance at seedling as well as anthesis stages has to be separately targeted. Thus, for developing new winter sorghum hybrids, female parental lines have to be diversified and improved for grain yield and percentage of seed set by crossing with promising germplasm lines identified in the study.

Performance of A1, A2, A3, A4(M), A4(G) and A4(VZM) cytoplasms based iso-nuclear sorghum hybrids for shoot fly resistance across-rainy and post-rainy seasons

Breeding for resistance to sorghum shoot fly in A1 CMS system has been only partially successful. To compare the alternate Cytoplasmic Male Sterility (CMS) systems for shoot fly resistance, 72 hybrids produced by crossing 36 A-lines carrying six diverse cytoplasms namely, A1, A2, A3, A4(M), A4(G), A4(VZM), each in six nuclear backgrounds with two common fertility restorers. The hybrids were evaluated during 2006 and 2007 rainy and post rainy seasons in shoot fly screening trials at ICRISAT. ANOVA indicated absence of overall cytoplasmic influence on dead hearts%. The general (GCA) and specific combining ability (SCA) estimates suggested that inheritance for deadhearts was governed by additive-type of gene action. For GCA effects, the A2 and A4(M) cytoplasms and for SCA effects, the A4(G) and A4(M) cytoplasms were superior over other cytoplasms. Overall, the A4(M) cytoplasm seemed to contribute to shoot fly resistance in hybrid combinations. However, use of all the six alternate cytoplasms should not increase the risk of shoot fly in commercial grain production.

Response of diverse groups of sorghum [Sorghum bicolor (L.) Moench] genotypes to low temperature stress at anthesis

Rapid productivity increases has not been realized in winter/post-rainy/rabi sorghum, an important food crop in the semi-arid tropical regions of India. The crop is dominated with varieties as poor seed set due to susceptibility to cold stress is noticed in the hybrids. Hence, before initiation of breeding program to bring in tolerance to cold stress, diverse group of breeding material that included 8 varieties, 7 maintainer lines, 5 restorer lines and a hybrid were screened for tolerance to cold stress in two dates of sowing for pollen viability and germinability apart from other agronomic traits. Date of sowing significantly influenced pollen germinability and the influence of the cooler night temperatures was more than the genetic background. In contrast, pollen viability had less phenotypic plasticity and highly heritable. The loss of grain yield (open panicle grain yield-selfed panicle grain yield) was about 5g/panicle in varieties while it was 1.9g/panicle in restorer lines and about 5.7g/panicle in B-lines. The loss in grain yield was highest in the hybrid at about 22.9g. Higher grain yields can be attained in the hybrid with improvement in the pollen viability and germinability. The germinability percentage was positively associated with selfed panicle weight, grain yield and harvest index while the viability percentage did not show such association. The germinability percentage was more linearly related in R lines followed by B lines and varieties.