Flowering Distribution within and among Grain Sorghum Panicles

Genetic differences of the grain sorghum [Sorghum bicolor (L.) Moench] flowering process have not been fully evaluated with respect to air temperature. Flowering duration (FD), i.e., the period of progressive tip to basal spikelet anthesis on a panicle, and flowering period (FP), i.e., the period between the first panicle at tip anthesis and last panicle at basal spikelet anthesis within a field, are important components of the sorghum flowering process. An irrigated field study with 10 commercially available hybrids was conducted in 1986 and 1987 to determine if variability in FP and FD was present. Dates when tip anthesis and basal spikelet anthesis occurred were recorded for 20 consecutive plants in a row. Panicle size (seed no., panicle length, and grain wt.) were determined for each panicle at maturity. Average FD, expressed as days or heat units (base temperature = 7 °C), was significantly different among genotypes. Maximum difference in FD was approximately 0.5 d and 15 heat units (hu). The FP was not significantly different among genotypes. The FD and FP were not correlated to panicle size. Average air temperatures less than 20 °C during anthesis of the 1987 ratoon crop lengthened FD and FP, suggesting anthesis may be delayed at temperatures higher than those required for plant growth.