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Over the past 20 years replicated field trials have been conducted on processing tomato varieties by the California Tomato Research Institute and the Israeli Ministry of Agriculture with the objective of identifying superior varieties. Because common check varieties were included in consecutive years, environmental effects could be factored out allowing an estimate of the genetic improvement due to breeding. The results indicate an average genetic gain for yield of 1.54%/yr for California and of 0.4%/yr for Israel. No significant genetic gain in brix was found for California, whereas for Israel, the data indicate an average increase of 0.53%/yr. For the derived trait brix × yield, the overall genetic gain ranged from 0.9%/yr in Israel to 1.5%/yr in California. A significant genetic gain of 1.15%/yr was determined for fruit color in California for the period 1977–87 and of 2.73%/yr for Israel during the years 1985–1995. The improvement in yield is partially due to the increase in the proportion of hybrids in the trials starting from the mid 1980's. The implications of the results for future tomato breeding are discussed.

Improved-processing tomato lines were produced by the molecular breeding strategy of advanced backcross QTL (AB-QTL) analysis. These near-isogenic lines (NILs) contained unique introgressions of wild alleles originating from two donor wild species, Lycopersicon hirsutum (LA1777) and L. pimpinellifolium (LA1589). Wild alleles targeted for trait improvement were selected on the basis of previously published replicated QTL data obtained from advanced backcross populations for a battery of important agronomic traits. Twenty three NILs were developed for 15 genomic regions which were predicted to contain 25 quantitative trait factors for the improvement of seven agronomic traits: total yield, red yield, soluble solids, brix×red yield, viscosity, fruit color, and fruit firmness. An evaluation of the agronomic performance of the NILs in five locations worldwide revealed that 22 out of the 25 (88%) quantitative factors showed the phenotypic improvement predicted by QTL analysis of the BC3 populations, as NILs in at least one location. Per-location gains over the elite control ranged from 9% to 59% for brix×red yield; 14% to 33% for fruit color; 17% to 34% for fruit firmness; 6% to 22% for soluble-solids content; 7% to 22% for viscosity; 15% to 48% for red yield, and 20% to 28% for total yield. The inheritance of QTLs, the implementation of the AB-QTL methodology for characterizing unadapted germplasm and the applicability of this method to other crops are discussed.

A pair of processing tomato (Lycopersicon esculentum Mill.) lines, nearly isogenic for the Tm-2a gene for resistance to tobacco mosaic virus, were grown in replicated trials under commercial production conditions in five locations worldwide. The lines were evaluated for 17 processing traits including fruit yield, size, soluble solids concentration, color, firmness, and viscosity. Eight of those traits differed significantly among the nearly-isogenic lines (NILs). Most notably, the NIL heterozygous for Tm-2a yielded, on average, 16% more than the NIL homozygous for the susceptible allele and 33% more than the NIL homozygous for Tm-2a. Viscosity was lower in the heterozygous NIL and the homozygous and heterozygous resistant NILs had softer fruit with larger stem scars compared to the homozygous susceptible NIL. These results indicate the presence of the Tm-2a locus affects many traits of importance for processing tomatoes and may be used, in the heterozygous state, to significantly increase yield. Whether the observed effects are due to the Tm-2a gene itself or genes associated via linkage drag could not be determined.

Anthers of 15 non-allelic male-sterile tomato mutants and their isogenic fertile lines were cultured in vitro. Anthers of one mutant ( ms 10 35 ) readily produced callus containing haploid cells and cells of higher ploidy levels. Conditions for the regeneration of plantlets from this callus were identified. Anthers of the remaining mutants and all the fertile isolines degenerated rapidly in culture. Role of the stage of microsporogenesis in successful anther culture is discussed.

Plants of the salt-sensitiveL. esculentum, the halophytic wild speciesL. pennellii, their F1 hybrids and the interspecific F2 generation were grown in Hoagland's liquid culture containing 100 mM NaCl and 6 mM K+. Analysis of the Na+, Cl- and K+ ions contents of the leaves showed, as observed also in previous studies, that the cultivated parent accumlated more K+ and less Na+ than the wild parent. A total of 117 F2 plants were assayed for 15 electrophoretically detectable isozyme markers which map to nine of the twelve tomato chromosomes. Four loci, all with a similar quantitative effect on Na+ and Cl- uptake, were identified by virtue of their linkage to isozyme markers. Two other loci were found to affect K+ uptake. This study demonstrates the potential value of using genetic markers in order to gain a better understanding of the genetic basis of quantitative traits associated with the response of plants to salinity stress.