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Abstract
The following is a brief review of our investigations on problems of germplasm acquisition, analysis, maintenance, evaluation, and use in the Lycopersicon spp. It is based entirely on our published research; hence, only a synopsis will be presented and appropriate citations made to direct readers to full presentation of results and analysis.
Abstract
The ghost mutant illustrated on the cover is one of the myriad monogenic variants known in the tomato. Although determined by a single gene (gh) of known chromosomal location, the homozygote is remarkably variable. It emerges with normal or slightly bleached cotyledons; the first true leaf is a mosaic of totally white and normal green areas; the subsequently developed leaves may have mostly green tissue, but are generally entirely white or light yellow phase; and either white or yellow phase can revert to patches or longitudinal stripes of the green phase. All selfed progeny from any of these phases are solely of gh phenotype. Although this mutant has elicited great interest as a possible example of transposable element activity, such activity has not been proven.
Abstract
Attention here will be confined to those non-profit groups that serve to exchange information and materials related to genetics and breeding of specific horticultural crops. Being independent of the formal scientific societies and having arisen electively according to demand, they are highly heterogeneous in regard to functions, organization, support, and even titles. In most respects this heterogeneity is commendable since the needs of the various groups differ, and each group develops a distinctive character. It is beyond the scope of this article to present all the details of each cooperative, but they will be compared in respect to the most important aspects of their structure and functions. I hope to avoid an excessive slant toward the Tomato Genetics Cooperative, with which I have been associated since its inception. Excluded from major consideration in this article are groups devoted exclusively to line testing (ex. Southern Tomato Exchange Program, STEP), those covering an entire crop group (e.g. Vegetable Improvement Newsletter, VIN; Small Fruit Workers, SFW), or those which are restricted regionally.
Abstract
Several characteristics of the cultivated tomato (Lycopersicon esculentum Mill.) and several wild relatives were explored as factors in resistance to the pink form of the potato aphid. Foliage volatiles of resistant and susceptible plants were found to be qualitatively similar but quantitatively different. Olfactometric tests revealed that the aphids did not react in any detectable way to the aroma variation conditioned by these quantitative differences. Epidermal hairs (non-glandular) of the normal genotypes were not a factor influencing degree of attack by the aphids. In the field the aphids avoided both an excessively hairy compound mutant stock Ln-Wom and the wild tomato relative L. hirsutum. However, under infestation in the laboratory the insects managed to feed on these plants. Pubescence in the normal genotype is not a factor affecting resistance. However, increase of hair density and length tends to restrict aphid feeding activity under field conditions. The presence of anthocyanin in the foliage did not inhibit aphids from feeding. No anatomical obstacles to reaching the feeding site, the internal phloem, were found in resistant accessions of the green-fruited species L. hirsutum, however, thick cortex in the stems might prevent aphids from reaching vascular tissue. Comparative analysis of foliage of susceptible and resistant plants revealed higher sucrose, lower quinic acid, and higher alanine and tyrosine contents and a trend toward higher total free amino-acid concentration in the former. Furthermore, susceptible plants were unique as a source of o-phosphoethanol amine.