Genetic variability in advanced Gezira population of sorghum (sorghum bicolor (l.) moench) at low input areas in Sudan

In Sudan, grain sorghum (Sorghum bicolor (L.) Moench ), is the most important cereal crop, in terms of total acreage, production and consumption. One hundred and twenty S 1 families were taken at random from an advanced random mating Gezira sorghum population (G S P-l) developed and improved [or six cycles using S !family selection, at Rain-fed Crop Research Centre for Arid and Semi Arid areas (RCRCASA) in the University of Gezira, Wad Medani Sudan. The study was conducted during two seasons (2004-2005) to study genetic variability in the population (GSP-l) at four rain-fed areas in Sudan namely; Gedarif University farm at Gcdarif northern marginal environment (200-300 mm) in 2004, (300-400mm) in 2004, Rahad rain-fed area at Gedarif Research Station at northern Gedarif in 2005 and Kasamor at Gedarif middle environment (500-600mm) in 2005. The design used was a modified Randomized Complete Block Design (RCBD) with replication nested within blocks. Genetic variability, expected genetic gains from selection, broad sense heritability, simple phenotypic and genotypic correlation coefficients, response to selection and yield stability were estimated for each of the following traits; days to 50% flowering (day), yield (KghE-1), leaf angle(deg), 1000 grains weight(gm) and plant height( cm). The combined analysis over environments revealed significant differences between environments, which indicated that four environments are contrasting for evaluating the genotypes. In average over environments the genotypes have shown significant differences for all traits studied, which mean that there is a wide range for selection. However GxE interaction was not significant for yield, indicating relative ranking of the genotypes remained constant and yield was stable over the four environments. The mean was 53.3 day for days to 50% flowering, 1448 for yield KghE-l, 28.4 deg C for leaf angle, 22.9 gm for 1000 grains weight and 85.9 cm for plant height. The highest expected gain from selection was given by plant height (3.1 %) and the lowest value was obtained by days to 50% flowering (0.21%). The highest heritability estimate was given by plant height, days to 50% flowering and yield (0.52 -0.50) and the lowest heritability value obtained by leaf angle (0.11), this indicates the fact that plant height, days to 50 % flowering and yield KghE-1 traits were targeted in the previous improvement of this advanced population, whereas leaf angle trait has not been targeted yet. Yield has a weak, but significant and positive correlation with all traits studied, except days to 50% flowering, where it has got negative correlation (-0.01). On genetic basis, the highest positive correlation coefficient values were obtained between 1000 grains weight with days to 50% flowering, yield with plant height and 1000 grains weight with leaf angle (0.88, 0.63 and 0.60 respectively). Yield KghE-l has got high positive correlation response, with days to 50% flowering, leaf angle, 1000 grains weight, plant height which indicated that yield, will be increased by 25, 148,413 and 55 KghE-l for everyone unit increase above the mean of each trait respectively and these are the most critical traits in the rain-fed areas characterized by low rainfall and short season. The Additive Main Effect and Multiplicative Interaction (AMMI) stability analysis with the first principal components (PCA1) axes for grain yield identified stable families as the families with a lower absolute PCA1 score which were 101, 95, 93, 96, 94, 103, 97, 102, 99,100, 104, 98 respectively, would produce a lower absolute GE interaction effect and would have a less variable yield across the four Gedarif sites. These could provide a good source for sorghum improvement in Gedarif rain- fed area