Potato breeding methods that utilize haploids of Solanum tuberosum group Tuberosum or group Andigena and 2n gametes exploit the genetic diversity, including both valuable traits and allelic diversity, available in exotic germ plasm. Three essential components are involved: (i) the wild and cultivated 2x relatives of the cultivated 4x potato are a valuable source of genetic diversity; (ii) haploids (2n = 2x = 24) of cultivars (2n = 4x = 48) are effective in capturing diversity (germ plasm enhancement); (iii) 2n gametes, resulting from first division restitution, are an efficient method of transmitting this genetic diversity to cultivated 4x potatoes. Heterosis for total and marketable tuber yield and specific gravity occurs in 4x families from crosses between 4x cultivars and 2x haploid Tuberosum × 'Phureja' hybrids. Selected 4x clones from relatively small 4x × 2x families have been released as cultivars based on their earliness and heat tolerance in the tropics. Other 4x clones from 4x × 2x crosses, where the 2x parents were haploid – wild species hybrids, have good yield, excellent tuber type, high specific gravity, low reducing sugars, storage quality, and stress tolerance. The seedling vigor, uniformity, and large tuber yields of progeny from 4x × 2x crosses also makes this an effective breeding method for producing potatoes from true potato seed. This breeding method is also being successfully exploited in alfalfa, red clover, sweet potatoes, yams and several species of grasses, fruits, and ornamentals.Key words: potato, haploids, 2n gametes, germ plasm, allelic diversity.

A study of spontaneous mutation in Arabidopsis thaliana was initiated from a single inbred Columbia founder; 120 lines were established and advanced 17 generations by single-seed descent. Here, we report an assay of reproductive traits in a random set of 40 lines from generations 8 and 17, grown together at the same time with plants representing generation 0. For three reproductive traits, mean number of seeds per fruit, number of fruits, and dry mass of the infructescence, the means did not differ significantly among generations. Nevertheless, by generation 17, significant divergence among lines was detected for each trait, indicating accumulation of mutations in some lines. Standardized measures of mutational variance accord with those obtained for other organisms. These findings suggest that the distribution of mutational effects for these traits is approximately symmetric, in contrast to the usual assumption that mutations have predominantly negative effects on traits directly related to fitness. Because distinct generations were grown contemporaneously, each line was represented by three sublines, and seeds were equal in age, these estimates are free of potentially substantial sources of bias. The finding of an approximately symmetric distribution of mutational effects invalidates the standard approach for inferring properties of spontaneous mutation and necessitates further development of more general approaches that avoid restrictions on the distribution of mutational effects.

Starch gel electrophoresis of plant proteins was used to identify purple loosestrife (Lythrum spp.) cultivars and weedy populations. Preliminary determinations were made as to what degree weedy loosestrife populations were related (or genetically similar) to populations of L. alatum, L. virgatum, and horticultural cultivars. Cluster analysis of the data indicated that native L. alatum was genetically different from all populations of purple loosestrife and cultivars examined. The L. salicaria and L. virgatum cultivars, as groups, were not genetically distinguishable from the weedy populations analyzed. Seven cultivars of L. salicaria origin analyzed as a group were not distinguishable from the eight cultivars of L. virgatum origin, indicating that separation by cultivar origin may not be feasible. While the two “groups” were not distinguishable, most individual cultivars could be distinguished from one another by isozyme phenotype. Genetic variation was high within populations of weedy purple loosestrife but low among populations, which is characteristic of polyploid, perennial plant species that are widely distributed. Geographic location did not consistently correlate with genetic similarity.

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