Floral Traits and Seed Production of Sorghum A-, B- and R-lines under Chilling Field Temperatures

In A-lines of sorghum ( Sorghum bicolor L. Moench), seed production under field conditions with manual pollination is generally lower than that in self-pollinated B-lines. This may be associated with floral differences. Six pairs of A/B-lines and four R-lines were evaluated during 2005 and 2006 at Montecillo, State of México (2240 m altitude). Rachis length, number of primary branches and fertile flowers per panicle, 100-seed weight, seed number, seed yield and seed set per panicle were evaluated. In the A-lines, the pistil characteristics were also measured and in the male-fertile lines, the size of anthers and the amount and size of viable pollen were recorded. Compared with the A- and B-lines, the R-lines exhibited significantly higher (P ≤ 0.05) numbers of flowers, seed set and seed yield per panicle and they also produced more pollen grains of larger size and with greater viability during their longer flowering period (FP). Between A- and B-lines, there were differences (P ≤ 0.05) in most of the yield traits, which also interacted with year. The proportion of viable pollen in B- and R-lines (75 %) was not considered to be a factor that might account for their low seed production. Chilling temperatures (3.5–8.4 °C) during the FP could have affected stigma receptivity in the three different line types and thus may have reduced seed set in the male-fertile lines.