Parental, F1, F2, and backcross generations of tomato (Lycopersicon esculentum Mill.) lines Morden MEL2668170G (MEL) and ‘Walter’ (WA) were screened as seedlings for resistance to verticillium wilt (Verticillium dahliae Kleb.) race 2. Disease reaction means, based on the number of leaves and cotyledons with symptoms 5.5 weeks after inoculation, were 2.7 for MEL and 4.6 for WA. Resistance in MEL appeared to be recessive with narrow sense heritability estimated at 0.25 or less. Disease severity was sometimes inadequate to avoid the selection of escapes in advanced generations. Analysis of F3 progenies, however, indicated 3 genes or less might be involved. Results suggest race-2 resistance can be maintained in advanced generations by the elimination of highly susceptible plants and by progeny testing to insure recovery of the most resistant individuals rather than escapes.
'Oregon Spring' and 'Santiam' are early maturing, Verticillium wilt-resistant tomatoes with compact growth habit and medium-large fruit that are mostly seedless. The cultivars differ in fruit size and maturity. 'Oregon Spring' bears fruits that are larger than those of 'Santiam', but ripen about 5 days later. They should be especially useful in cool-summer areas where seedlessness and relative earliness will be maximized. 'Oregon Spring' and 'Santiam' will be most useful for home garden, roadside stand, and limited local market, since they lack the fruit firmness required for commercial handling.
Size and number of plots is an important consideration for strawberry breeders and other researchers engaged in the evaluation of strawberry cultivars. Edgar (2) found at East Mailing that plots of about 50 plants planted on the square were best, but Taylor (3) considered the variability in Edgar’s plots to be abnormally low, and advocated plots of 24 plants arranged in a twin row. He considered that seven replicates were necessary to measure a 20 percent difference at the 5 percent level of probability. Baker and Voth (1) in California considered 3 plots of 50 plants or 8 of 25 plants necessary to reduce heterogeneity to an acceptable level for scoring clones for resistance to Verticillium wilt in a “wilt nursery.” All of these researchers were working with strawberries on the hill system, whereas the matted row system is standard in Eastern North America.
Abbreviations: Fol 1 and 2, Fusarium oxysporum f. sp. lycopersici races 1 and 2; Forl, Fusarium oxysporum f. sp. radicis-lycopersici; Mel, Meloidogyne incognita; TMV, tobacco mosaic virus; Verd, Verticillium dahliae. 1 Assistant Professor
An olive rootstock planting was established in Tulare County, California in 1954 using 10 different rootstocks with ‘Sevillano’ as the scion variety. Verticillium wilt, a major problem in California olive production, became strongly established in this planting, affecting trees on the different rootstocks to a markedly different degree. All trees on 2 of the rootstocks, Olea ferruginea Royle and Forestiera neo-mexicana Gray were killed. No trees on a clonal rootstock, Olea europaea, ‘Oblonga’ were affected, while trees on the 7 other rootstocks showed intermediate survival percentages. Over a 15-year period, tree size and yields were influenced by the rootstock. ‘Sevillano’ trees, on their own roots, were the smallest as measured by trunk cross section area. There was no pronounced effect of rootstock on fruit size.
In another olive planting in Tulare County, California, the effect of various interstocks, inserted during a top-working operation, on the behavior of the scion cultivar was determined. No Verticillium wilt was apparent in any of the trees in this experiment. Each of 3 genetically dwarfed clonal stocks caused a significant dwarfing influence on the scion cultivar and a reduction in yields, in comparison with the scion cultivar itself used as an interstock. No influence on fruit size occurred. Similar results were noted with Olea chrysophylla Lamk. as an interstock but with severe constriction of the interstock tissue.
We gratefully acknowledge Sara Olson for helping to develop the verticillium resistance screening protocol. We also thank Dennis Johnson and Linda Ciuffetti for providing V. dahliae cultures, and J. Brent Loy and Rosanna Freyre for helpful
Previous studies have demonstrated significant genetic variation for susceptibility to verticillium wilt, caused by Verticillium dahliae, among strawberry (Fragaria ×ananassa Duch.) genotypes adapted to California growing conditions. These evaluations have been conducted using a conidial root-dip inoculation procedure; valid application of this method in a breeding program assumes the reaction of inoculated plants will be predictive of their response to infection by more natural means. To test this expectation, we evaluated the responses of plants representing eight strawberry genotypes that were either root-dip inoculated prior to being transplanted into a fruit production field or were transplanted into soil artificially infested with pathogen propagules (microsclerotia). Both inoculation methods revealed significant variation among genotypes in all 3 years that tests were conducted and the absence of significant genotype × treatment interactions demonstrate similar rankings of genotypes with both methods. However, based on statistical repeatability, the root-dip inoculation method was more consistent over time (R = 0.759) than the soil inoculation method (R = 0.510).
Two studies were performed to evaluate techniques for screening verticillium wilt of Capsicum annuum L. The first study tested inoculation methods. The original method involved mixing the inoculum with planting medium in a cement mixer for 1 h. Seeds then were planted in the infested medium. In the new technique, inoculum is poured directly into the row, and seeds are placed directly on top of the inoculum. Inoculum levels of 2000 and 1000 mcrosclerotia/g of soil were tested in the new “in-row” method. The disease severity of the “in-row” plants was significantly less than the plants inoculated by the original method. A significant difference remained between resistant and susceptible lines. There was no difference between inoculum levels. The second study compared three commercial planting media to the standard soil used in previous screenings. Disease severity did not differ among media, and all media showed significant differences between resistant and susceptible C. annuum lines.
Temperature, cultivar, locus of inoculation, and prior-inoculation (inoculation 24 hr earlier with 3 nonpathogenic fungi) affected the expression of fusarium wilt caused by Fusarium oxysporium f. niveum (E.F.Sm.) Snyder & Hansen, in watermelons. Prior inoculation with Helminthosporium carbonum Ulktrup was found to be more effective in cross protection than were Fusarium oxysporium f. lycopersici (Sacc.) Snyder & Hansen, or Verticillium alboatrum Reinke & Berth. Temperatures of 27°C resulted in more fusarium infection than at 20° and obscured the expression both of genetic resistance and resistance induced by the prior-inoculations. Induced resistance increased plant survival and plant growth for 3 cultivars in field trials, but possibly produced deleterious effects in a resistant cultivar.
‘Ozark Pink’ VF is an indeterminate, pink-fruited tomato (Lycopersicon esculentum Mill.) developed at the Univ. of Arkansas to replace ‘Traveler 76’ (2), which is susceptible to verticillium wilt. ‘Ozark Pink’ provides the excellent flavor quality of traditional Arkansas pink tomatoes with improved fruit size and disease resistance over ‘Traveler 76’. Fruits also are larger and firmer than ‘VF Pink’ (3), which was grown primarily in southeastern Arkansas. ‘Ozark Pink’ is adapted to stake culture and vine-ripe harvest for local market, shipping short distances and for home gardens throughout Arkansas and the Ozark Mountain area. Pink cultivars remain the most popular type sold as bedding plants and at roadside stands in Arkansas, although part of the commercial acreage now grows red-fruited cultivars.