Sorghum cold tolerance, pollen production, and seed yield in the central High Valleys of Mexico.

摘要

Sorghum (Sorghum bicolor L. Moench) production at altitudes higher than 2200 m, where early morning temperatures close to 8°C prevails during the growth cycle, is restricted by its susceptibility to male sterility induced by low temperatures. Cold-tolerant (CT) lines and hybrids have already been developed in Mexico. Three field experiments, each one with 64 genotypes were initially established, to evaluate the potential of CT germplasm in the adaptation and adaptability of grain sorghum in the Mexican High Valleys (Osuna et al., 2000). From each experiment, we selected three B and three R cold-tolerant lines, from the Sorghum Improvement Breeding Program of the Colegio de Postgraduados; and a similar number of cold-susceptible (CS) sorghum lines from the Sorghum Program of the National Research Institute of Forestry, Agriculture, and Animal Husbandly (INIFAP in Spanish), as well as 35 F1 crosses representing the combinations CTxCT, CTxCS, CSxCT, and CSxCS, plus three controls. Data from these 50 genotypes were analized under a randomized complete block design with two replications. The objectives were to determine the effect of low temperatures on production of fertile and sterile pollen, stigma receptivity, and seed production in selfed and open pollinated panicles. The relationships among these variables were also evaluated. Results show that low temperatures affected the quality and reduced the amount of pollen produced, and possibly modified stigma receptivity. The severity or extent of such effects depended on the degree of cold tolerance of the genotypes. Open pollinated panicles produced more seed than selfed panicles, so cross pollination should be considered as a frequent phenomenon in sorghum grown under low temperature environments. Cold-tolerant lines produced more pollen, higher percentage of fertile pollen, lower percentage of sterile pollen, and higher amount of seed under self and open pollination than CS ones. Partially CT hybrids tended to behave as CT ones. Genotypes did not show a significant correlation between production of fertile pollen and grain yield, because of the high proportion (more than 50%) of cross pollination observed in some CS genotypes, under low temperature conditions during the pre-boot growth stage.