Characterization of Mating Systems in tea (Camellia sinensis (L.) O. Kuntze)

Abstract

Knowledge of the predominant mating patterns in plant species is important for ifie development of efficient breeding strategies. In this respect, an estimation of the rating system parameters for understanding of the genetic structure in Camellia sinensis '->-5 conducted. Three experiments were set-up among eight C. sinensis genotypes in four riclonal isolated seed orchards located in two sites, namely Kericho and Kerugoya. An :’.~\'itr0 germination method was used to study variation in pollen viability (pollen germination) over three flowering seasons during the year 2005. Significant variation in pollen viability among the eight genotypes indicated male gametophyte competition. A significant genotype by environment (location) interaction and a positive correlation between the pollen viability and temperature was observed. Four pollination methods, namely: selfing through bagging; controlled cross-pollination; open-pollination; and controlled self-pollination were compared. The evaluation of crossing success was based on abortion rates, fruit/seed set, seed weight/number per fruit and seed germination percentage. Open pollination had the highest fruit/seed set (44.8%) followed by controlled cross-pollination (32.5%), selfing through bagging (23.7) and lowest in controlled self-pollination (20.6%). Based on molecular markers (RAPD and ISSR), mating parameters of 30 open pollinated breeding progeny arrays of the 6 genotypes were estimated. The mixed mating system estimates obtained (t,,, = 0.99) indicated that C. sinensis is predominantly outcrossed suggesting that expected levels of genetic variation for open-pollinated families are likely to be maintained. The low rm-1, (0.024 i 0.094) indicated negligible biparental inbreeding. Likewise, low estimate of correlation of patemity (rp = 0.070) indicated that many of the offsprings do not share same paternal genitor despite the isolation of the two putative parents which is indicative of high pollen contamination in the isolated orchards. These results suggest that a review of the current isolation distance (6m between breeding genotypes) is necessary so as to increase pollination efficiency between the two isolated clones and minimize extraneous pollen contamination