Heterologous expression of taro cystatin protects transgenic tomato against Meloidogyne incognita infection by means of interfering sex determination and suppressing gall formation.

Plant-parasitic nematodes are a major pest of many plant species and cause global economic loss. A phytocystatin gene, Colocasia esculenta cysteine proteinase inhibitor (CeCPI), isolated from a local taro Kaosiang No. 1, and driven by a CaMV35S promoter was delivered into CLN2468D, a heat-tolerant cultivar of tomato (Solanum lycopersicum). When infected with Meloidogyne incognita, one of root-knot nematode (RKN) species, transgenic T1 lines overexpressing CeCPI suppressed gall formation as evidenced by a pronounced reduction in gall numbers. In comparison with wild-type plants, a much lower proportion of female nematodes without growth retardation was observed in transgenic plants. A decrease of RKN egg mass in transgenic plants indicated seriously impaired fecundity. Overexpression of CeCPI in transgenic tomato has inhibitory functions not only in the early RKN infection stage but also in the production of offspring, which may result from intervention in sex determination.

RAPD markers for the identification of yield traits in tomatoes under heat stress via bulked segregant analysis.

Tomato production is limited to a large extent by climates with high temperatures. Yield-related traits in tomatoes are generally thought to be quantitative inherited traits that are significantly affected by variation in environmental factors. Breeding for heat tolerance is restricted due to the complexity of the traits. The objective of this study was to identify random amplified polymorphic DNA (RAPD) markers linked to heat-tolerance traits in tomatoes under heat stress. Forty-three F(7) recombinant inbred lines (RILs) derived from a wild cross between CL 5915 (heat-tolerant) and L4422 (heat-sensitive) were obtained and scored for flower number, fruit number, fruit set, fruit weight and yield under screen house conditions during the hot (summer) season of 2003. The distributions of average fruit weight, fruit number, fruit set and yield in the F(7) population were strongly skewed towards heat susceptibility, characteristic of L4422. Significant positive correlation was observed between fruit weight and yield, and between fruit number, fruit set and yield. However, the increase in yield and fruit set by selecting for large flower number may be fairly minor due to non-significant correlation between these traits. Selecting for flower number may not be a useful tool for improving yield under heat stress. A total of 200 RAPD primers were screened, among which 14 were identified as associated with heat-tolerance using bulk segregant analysis (BSA) based on the F(7) population grown in a heat-stressed environment. Some RAPD markers were unique to one specific trait, and others were linked to two traits. All markers for heat tolerance related traits had positive gene effects as a result of the contribution of the CL5915 gene that bolstered these traits. One hundred F(2) plants derived from the same parents (CL5915xL4422) were grown in the same location during the summer of 2004 to test for the stability and reliability of the 14 markers identified. Selection for the desired heat-tolerance genotypes corresponded well with targeting heat tolerance traits using the selected heat tolerance RAPD markers identified. Marker-assisted selection (MAS) for heat tolerance may be efficiently conducted by selecting individuals that contain high fruit number, high fruit weight, and high yield markers (P06, X01, D06 and D11), which would thus facilitate conventional breeding using CL5915 as a donor parent.

Diallel Analysis of Bacterial Wilt Resistance in Tomato Derived from Different Sources.

Bacterial wilt, caused by Ralstonia solanacearum, is a major constraint to tomato production in the tropics and subtropics. Most bacterial wilt-resistant tomato cultivars have not shown consistently high resistance levels over locations. The objective of this study was to determine whether combining resistance derived from different sources would result in F1 progenies with resistance greater than that of the parents. Five bacterial wilt-resistant tomato lines or accessions (CL5915, L285, CRA84, H7997, and GA219), each derived from different resistance sources, and a susceptible processing tomato line (UC204A) were crossed in all combinations without reciprocals. Parents, F1 progenies, and F2 progenies were evaluated in greenhouses at three locations (Taiwan, Philippines, and Indonesia) for percent survival 6 weeks after drench inoculation with virulent local strains of R. solanacearum. Percent survival means over locations were 17.4 to 83.0 for parents and F1 progeny and 16.2 to 75.0 for parents and F2 progeny. The percent survival means over locations of L285 × H7997 were highest among crosses in the F1 (83.0) and F2 (75.0) generations but were not significantly greater than that of H7997. Highly significant mean squares were found in the F1 and F2 progenies for general combining ability (GCA) and GCA × locations. Positive GCA effects over locations were detected for H7997, CRA84, and L285, indicating that progeny with those lines as parents showed bacterial wilt resistance that was greater than the average of all crosses. Only H7997, however, had positive GCA effects estimates at each location for each generation, and its GCA effects estimates over locations were significantly greater than those of the other parents in the F1 and F2 progenies. Among this set of parents, H7997 is the best source to develop bacterial wilt-resistant progeny. We did not observe statistically significant increases in resistance by combining different resistance sources. However, the presence of large GCA variances suggests that hybridization of parents that have high GCA for bacterial wilt resistance, such as H7997, CRA84, or L285, followed by selection in segregating populations might yield inbred progeny with resistance greater than that of the parents.