Germination patterns in coconut populations (Cocos nucifera L.) in Mexico

Abstract

Lethal yellowing disease has drastically affected the coconut populations on the east coasts of Mexico and is threatening to invade all the production areas in Mexico. For the purpose of defining the existence of genetically differentiated coconut populations that eventually could have a differential response to this disease, we studied the germination patterns in 20 representative coconut populations using 90 nuts per population in three lots under similar growing conditions. Following the emergence of the leaf through the plumuler fissure, the following were calculated weekly: (1) percent emergence of the first leaf, percent mortality between germination and emergence, and percent germination capacity; (2) time required to reach 25%, 50%, 75%, and 100% of germination; (3) mean time to complete germination, coefficient of the rate of germination, and uniformity of germination; and (4) sigmoid curve parameters of accumulative percent germination, adjusted to a model of nonlinear regression (log scale). The results showed three population groups: (a) with early and uniform germination; (b) with early and heterogeneous germination, and (c) with late and heterogeneous germination. The same population groups were previously observed using fruit morphological traits. This suggests the presence in Mexico of three tall coconut genotypes. Late and heterogeneous populations have been almost totally eliminated by the disease and some precocious populations have been shown very low levels of mortality. This suggests a correlation between precocity and resistance. The geographical distribution of the ecotypes suggest that the mortality will be deferential when the disease arrives to the other coconut producing areas in Mexico.