REPRODUCTIVE PHENOLOGY IN A PROGENY TEST OF Pinus greggii var. australis

Abstract

Seed orchards should provide sufficient seed at an early age with superior genetic quality and at regular intervals. Lack of flowering synchrony generates decrease in genetic diversity of the seed lot and a high percentage of abortive ovules and empty seeds. This work reports synchrony and temporal variation in floral phenology in a progeny test of Pinus greggii var. australis set at two sites in Central México: Cuautepec, Hidalgo and Terrenate, Tlaxcala. These tests turned into sexual seed orchards. Twenty-three half-sib families, with at least four trees per family per site, from five provenances were monitored for two years. Observations were conducted on the whole tree crown every two weeks from March to June of 2012, and twice a week between February and June of 2013 on 24 selected buds per tree, based on full crown, crown layers and branch orientation. Stages of strobili development were identified and the start and end dates of male and female flowering, and their durations were determined. Synchronization of flowering periods (PO₀) was 0.31 in Terrenate 2012 and 0.34 in Cuautepec 2013, considered normal values taking in account the sexual origin of the test; however, in Cuautepec 2012 it was considerably high (0.57). All families showed some degree of synchronization with each other, except for Terrenate 2012. Flowering in Cuautepec was significantly earlier and longer than in Terrenate 2012. There was no female flowering, and male was very low in Terrenate 2013 which was associated with drought. Only significant variation between families was detected in Terrenate for most variables, and large variation within families. Significant differences between crown layers, but not for branch orientation in pollen dispersion were observed.