The influence of cryogenic pollen storage on fruit set and seed production in tomato (Lycopersicon esculentum Mill.) was investigated. Flowers pollinated with pollen samples stored for 5 weeks at –80C, with or without 20 h precooling at 4C, had similar fruit set and number of viable seed per fruit as those pollinated with fresh pollen. Pollen samples, which were repeatedly cooled (–80C) and warmed (to 22 to 24C) for up to six cycles, continuously maintained the same viability as the fresh pollen. When cryogenically stored pollen of L. esculentum 2-837, LA359, LA3198, and LA3199 were used to pollinate LA359, the number of viable seed formed per fruit differed significantly. Results of this study suggest that pollen cryopreservation can be used successfully for tomato breeding and germplasm storage.
Erik J. Sacks and Dina A. St. Clair
José G. Levy and Dina A. St. Clair
High temperatures during flowering have been implicated in reducing seed set and fruit set in tomatoes (Lycopersicon esculentum). Pollen viability and vigor were studied by measuring in vitro germination and pollen tube development in pollinated pistils of four processing tomato cultivars under normal (25° C day/15° C night) and high (32° C day/23° C night) temperatures. Preliminary studies were carried out to determine the length of pollen tubes in styles collected in times ranging from 3 to 48 hours after pollination. Under normal temperatures the pollen tubes reach the end of the style between 12 and 18 hours. At high temperatures there are fewer pollen tubes moving through the style and the time to reach the end of the style is longer. In pollen vigor studies, crosses were made between pollen and pistils of plants grown under different temperature treatments, then pollinated pistils were collected at 4, 8 and 12 hours after pollination. There were differences in in vitro pollen germination percentage and pollen tube length in the pollinated pistils, suggesting that high temperatures act to slow down pollen activity.
Steven R. Triano and Dina A. St. Clair
The inbred backcross (IBC) breeding method is being used to introgress genes controlling high fruit soluble solids from a wild tomato species (Lycopersicon cheesmanii f. minor) into a California processing tomato cultivar (Lycopersicon esculentum cv. UC204B). One IBC tomato population (i.e. P1: 106 lines) is being used to map quantitative trail loci (QTL) for soluble solids and other traits. A genetically related but independently generated IBC population (i.e. P2: 96 lines) is being used to lest the efficiency of QTL-linked RPLPs for indirect marker-assisted selection (MAS) to improve soluble solids. P1 was analyzed for fruit quality traits in a replicated field design over 2 years. Twelve P1 lines were significantly greater than UC204B for soluble solids and also had acceptable fruit weights and horticultural traits. All twelve lines have been publicly released for further breeding efforts. In P1. we have identified RPLP markers that have significant correlations to QTL. Some of these markers map to regions previously reported by other researchers to contain QTL for the same traits. We will use 70-80 markers spaced approximately 10-20 cM apart across the genome to screen PI and map QTL. The RPLP analyses are currently in progress. P2 was replicated for one year using the same field design as P1. and analyzed for the same traits. P2 will be screened with QTL-linked RFLPs identified in P1 to test the consistency of QTL locations between independently derived populations. P2 lines selected using RFLP data will be compared to P2 lines identified by classical selection indices. This will indicate if MAS for QTL is effective in a population (P2) genetically independent from the mapping population (P1).