Vivipary incidence in corn (Zea mays L.) hybrids as affected by precipitation, relative humidity and air temperature under Isabela, Philippines condition

The occurrence of vivipary in five yellow corn hybrids as affected by Agro-phenotypic characteristics, endogenous growth hormones, and weather factors imposed through four planting schedules and two growing locations, with varying altitude in Isabela were investigated during 2008-2009 dry season. The susceptible hybrid check (Hybrid 5) has significantly higher percent vivipary (incidence x severity) (7.09%) than the tolerant hybrid check (Hybrid 1) (0.74%). Percent vivipary peaked during the first batch of planting, where the coldest temperature (24.53 degC), and highest RH (83.6%) and precipitation (24.13 mm) occurred during the grain development stages, in the high elevation (126 masl) area in Brgy. [village] Fugu, Jones, Isabela. Relative humidity and precipitation were positively correlated with percent vivipary particularly during the dough stage (31-35 days after silk emergence, DAS), with r values of 0.43 and 0.28, respectively. Average daily air temperature, on the other hand, was negatively correlated with percent vivipary during the entire embryogenesis period. Based on the 78 predictor variables for the occurrence of vivipary, high RH and precipitation during the early embryonic development period (blister to dough stages) were identified to have the largest contribution to vivipary incidence, as shown in the equation: Predicted Percent Vivipary (incidence x severity) = - 61.74 + 0.76 (RH at 31-35 DAS) + 4.19 (Precipitation at 13-15 DAS) - 3.15 (Precipitation at 16-20 DAS). The gibberellic acid (GA) concentration and the abscisic acid (AGA) to GA ratios of corn kernels at 32 DAS in the 1st batch of planting in Fugu, Jones, Isabela did not differ among test hybrids, while significant differences were obtained in ABA concentration were obtained among the five test hybrids, hence, the role of endogenous ABA on the percent vivipary was not established. The GA concentration obtained in Fugu, Jones were relatively higher than in Lalog 1, Luna, which could partly explain the higher percent vivipary, when planted under higher elevation and colder environment compared with the negligible vivipary incidence observed under lower elevation and hotter growing area. Based on the information generated, the behavior of GA and ABA under varying climatic variables needs further investigation. Vivipary had generally loose, negative correlation with Fusarium ear rot (- 0.115) and yield (- 0.06). Likewise, vivipary is loosely correlated with Diplodia ear rot (0.055), husk cover rating (0.004) and ear angle (0.052).