Tolerância ao retardamento de secagem em sementes híbridas de milho em função dos parentais e da temperatura

Abstract

Corn production in Brazil has increased at each harvest and one of the reasons is the use of high-quality seeds. Seeds quality can be reduced from the point of physiological maturity, especially if the seeds remain in the production field. For this reason, corn seeds are harvested on the cob close to the point of physiological maturity, which implies high humidity. The high water content at the time of harvest requires attention until drying, so that the quality is not impaired. Thus, one of the bottlenecks in production today is the period between the harvest and the beginning of its processing; as it is prolonged, there is a delay in drying, which can damage the quality of the seeds. The objective of this study was to evaluate the effect of genetic makeup, parental arrangement, tolerance to the drying delay of the ears, the physiological quality and the enzymatic expression of the seeds. Two experiments were conducted. In the first one, ears from each genotype were harvested close to the point of physiological maturity (about 35% humidity), identified as lineage 1 (L1), lineage 2 (L2), hybrid HB (maternal parent L1 and paternal L2) and reciprocal hybrid (RH), with inversion between parents. After manual harvesting of the ears, they were submitted to six waiting times until they were submitted to artificial drying (10, 18, 24, 28, 32 and 40 hours) at two temperatures (42 and 48 °C). Completely randomized design (CRD) with a 4 x 6 x 2 factorial arrangement was used. In the second experiment, with the same genotypes and procedures, the ears were submitted to the waiting period between harvest and drying for 10, 24 and 40 hours under a constant temperature of 48 °C in the delaying environment, using CRD and 4 x 3 factorial. After the delaying period, the seeds were artificially dried to 13%. In both experiments, the physiological quality was evaluated by means of paper germination test, crop emergence, and cold test. In the second experiment, the abundance in the seeds of late embryogenesis abundant proteins (LEA proteins) and expressions of the enzyme α-amylase (α-AM) were also evaluated. The data were submitted to an analysis of variance F (p <0.05), Tukey's test at 5% probability, and analysis of polynomial regressions. The lineages were more sensitive to high temperatures and drying delay compared to hybrids; L2 was more susceptible. The temperature of 42 °C affected only the quality of the L2. Lineages reduced quality in the first 10 hours of drying delay at 48 °C. The quality of the hybrid seeds was not affected within 40 hours of delay at 42 °C; however, at 48 °C the delay was harmful. The positioning of the lineages affected the tolerance to the drying delay of hybrid seeds. Susceptible lineages should not be used as female parents as they affect the tolerance of hybrid seeds. With extended drying delay period, there was greater abundance of LEA proteins, mainly in the lineages. The seeds of the lineage most susceptible (L2) to drying delay had lower expressions of alpha amylase.