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- Author or Editor: R. W. Robinson x
Cucurbita ecuadorensis is a valuable source of multiple virus resistance. It is resistant to zucchini yellow mosaic virus (ZYMV), papaya ringspot virus (PRSV), watermelon mosaic virus, tobacco ringspot virus, squash mosaic virus, and cucumber mosaic virus (CMV). Its virus resistance can be transferred to squash and pumpkin, but sterility barriers must be overcome. The cross Cucurbita maxima× C. ecuadorensis can readily be made, and there is no need for embryo culture. Pollen fertility of the hybrid is somewhat reduced, but sufficient for producing F2 seed. Segregation for sterility occurs in the F2, but selection can be made for fertile plants that are homozygous for virus resistance. Cucurbita ecuadorensis is much more distantly related to C. pepo than to C. maxima, and there are more formidable barriers in this interspecific cross. The cross is very difficult to make with some C. pepo cultivars, but other cultivars are more compatible. Viable seed were not produced, but hybrid plants were obtained by embryo culture. Although both parents were monoecious, the hybrid was gynoecious. Male flower formation was induced by treating the hybrid with Ag or GA, but they were male-sterile. F2 seed was not obtained, but backcross seed was easily produced by using the interspecific hybrid as the maternal parent in crosses with C. pepo. The most refractory barrier was achieving homozygosity for ZYMV resistance. Disturbed segregation occurred in succeeding generations and the progeny of most resistant plants segregated and were not uniform for resistance. This and other barriers to interspecific gene exchange were overcome and a summer squash variety homozygous for resistance to ZYMV, PRSV, and CMV is being released this year.
Summer squash (Cucurbita pepo L.) cultivars were compared for ability to set parthenocarpic fruit. Some cultivars set no parthenocarpic fruit and others varied in the amount of fruit set when not pollinated. The degree of parthenocarpy varied with season, but the relative ranking of cultivars for parthenocarpy was generally similar. Cultivars with the best parthenocarpic fruit set were of the dark green, zucchini type, but some cultivars of other fruit types also set parthenocarpic fruit. A summer squash cultivar was developed that combines a high rate of natural parthenocarpy with multiple disease resistance. Yield of summer squash plants grown under row covers that excluded pollinating insects was as much as 83% of that of insect-pollinated plants in the open.
Abstract
Foliar application of 50 or 100 ppm 2-chloro-9-hydroxyfluorene-9-carboxylic acid (chlorflurenol) to plants of cucumber (Cucumis sativus L.) increased the number of fruit per plant 2- to 3-fold at a single harvest, particularly the more valuable small fruit. Higher and lower concentrations were less effective, and repeated applications were often more effective than a single application. In 2 of 4 field trials there were significant increases in value of treated over untreated plots, and in none of the trials was fruit shape affected.
Abstract
Five hundred ninety accessions of Citrullus lanatus, obtained from 42 countries, were exposed to natural infection with Sphaerotheca fuliginea (Schlecht) Poll. Only one line, P.I. 269677 from Belize, was highly susceptible. The fungus attacked all aerial parts of plants of this line, including fruits. All other lines, including those from areas of the world where powdery mildew of watermelon commonly occurs, were resistant or tolerant to the race of the fungus prevailing in NY.
Abstract
Soil application of (2-chloroe thyl)phosphonic acid (ethephon) strongly promoted pistillate flower formation of cucumber. Soil treatment had a prolonged effect, for plants transplanted 4 weeks after the chemical was added to the soil were greatly modified in growth and development.
Abstract
Recommended rates of (2-chloroethyl)phosphonic acid (ethephon) application did not prevent staminate flower formation on summer squash (Cucurbita pepo L.) sufficient to permit hybrid seed production without defloration. The field experiments were conducted in commercial fields in which flower development occurred during warm long day conditions, which promote maleness in squash. A strongly female ‘Cocozelle’ inbred, a strongly male ‘Straightneck’ inbred and a very strongly male ‘Crookneck’ inbred were treated at several seedling stages with rates up to 600 ppm ethephon. Two applications of 400 to 600 ppm ethephon resulted in development of the fewest staminate flowers without significantly reducing seed yield or quality. The ‘Crookneck’ inbred was least responsive to ethephon.
Abstract
An isogenic line, differing from ‘New Yorker’ tomato (Lycopersicon esculentum Mill.) by being homozygous for the crimson gene (ogc ), had 60% less provitamin A due to reduced β- and γ-carotene.
Abstract
A 6-year (1975-1980) survey established that broad bean wilt virus (BBWV) was second only to cucumber mosaic virus (CMV) in causing destructive diseases in leading lettuce cultivars grown in New York State. Conversely, the widespread usage of certified seed had drastically reduced the occurrence of lettuce mosaic virus (LMV). Screening for resistance revealed that a number of accessions of Lactuca sativa and a few of L. virosa were tolerant to BBWV. Tolerant plants, although infected with the virus, remained symptomless or responded with a mild and often transient chlorotic mottle.
Abstract
Lycopersicon esculentum Mill. cv. New Yorker, Solanum pennellii Corr. PI 246502, and 16 stable breeding lines of horticultural type derived from this cross were evaluated under saline (0.1 m NaCl) and control conditions. The breeding line population exhibited a much wider range of salt tolerance than that found in the cultivated species. Relative ability to regulate sodium accumulation in the leaves was significantly correlated with growth under saline irrigation. Absolute levels of foliar sodium or chloride accumulated under saline irrigation were not significantly correlated with plant growth. Regulation of ion accumulation was assessed as the ratio of foliar ionic content in saltgrown plants to foliar content in control plants, a value which we define as ion regulation index (IRI). A low index indicated regulation of accumulation of a particular ion. Regulation of ion uptake is interpreted as reflecting an effective homeostatic system. The homeostasis was attributed to tomato, and salt tolerance improvement occurred only if the requisite homeostasis was combined with other factors conferred by S. pennelli. Information regarding occurrence and possible mechanisms of this type of salt tolerance is reviewed.
Abstract
No significant resistance to verticillium wilt (Verticillium dahliae Kleb) was found in 59 eggplant (Solanum melongena L.) accessions, in a sexual hybrid between S. melongena and S. integrifolium, or in eight somatic hybrid clones between S. melongena and S. sisymbriifolium. A relatively high degree of resistance was observed in accessions of S. aculeatissimum, S. scabrum, and S. sisymbriifolium. All 58 accessions of S. gilo tested were susceptible, as were all accessions of S. incanum, S. integrifolium, S. laciniatum, S. macrocarpum, S. mammosum, and S. nodiflorum.