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Abstract

Strawberry (Fragaria × ananassa Duch.) seedlings of a 4-parent diallel and runner plants of their parent cultivars were inoculated with naturally occurring complexes of mottle, mild-yellow edge, and crinkle viruses by infesting plants with viruliferous aphids. The parent cultivars, chosen to represent a range in tolerance to complexes of these viruses, were ‘Hood’, ‘Olympus’, ‘Rainier’, and ‘Totem’ (listed in order of increasing tolerance). Virus inoculation reduced seedling plant vigor, petiole length, leaflet width, leaf dry weight, and parent plant vigor, but increased the numbers of leaves per plant of both seedlings and parents in the greenhouse. After growing in the field, virus-tolerance ratings of inoculated seedlings were lower than ratings of control seedlings. General combining ability constants for inoculated seedlings were similar, in rank and separation, to those reported by previous investigators. Field virus-tolerance ratings were lower than controls for inoculated plants of only one parent (‘Olympus’) and were higher than controls at the final evaluation for inoculated plants of a 2nd parent (‘Totem’). Genotypic differences among seedlings and parents confounded the effects of virus inoculation in both the greenhouse and the field. Petiole length in the greenhouse was correlated most consistently with subsequent field virus-tolerance ratings. The mean virus-tolerance ratings of inoculated seedlings, selected on the basis of petiole length, was higher than the rating of all inoculated seedlings and did not differ from the rating of control seedlings.

Open Access

Abstract

Seedlings of strawberry (Fragaria × ananassa Duch.) from 29 crosses were evaluated in a field trial over a 2½-year period for tolerance to a complex of viruses. The seedlings and plants of the parent clones were subjectively rated for tolerance on the basis of vigor, runnering, and appearance of virus symptoms. ‘Totem’ and ‘Aiko’ produced the highest percentage of tolerant-appearing seedlings, while ‘Olympus’, ‘Belrubi’, and ‘Hood’ produced the highest percentage of susceptible seedlings. At the end of the trial, when the symptoms were most severe, heritability for tolerance was 0.73. Specific combining ability variance was much smaller than general combining ability variance, indicating that a high proportion of genetic variance was additive. Therefore, rapid progress in breeding for tolerance can be expected from selecting parent clones on the basis of phenotypic performance.

Open Access

Abstract

Strawberry (Fragaria × ananassa Duch.) seedlings were planted in a greenhouse at 3- to 4-week intervals and simultaneously inoculated at ages 80, 101, 129, or 157 days with either of two naturally occurring virus sources each of which contained a mottle, mild yellow edge, and crinkle virus complex. Inoculation by aphids with either virus source reduced vigor, petiole length, leaflet width, stolons per plant, and vegetative dry weight of plants in the greenhouse. The tendency of virus inoculation to reduce vigor and petiole length was inversely proportional to increasing seedling age. In the field, inoculated seedlings were also less vigorous than control seedlings. Virus source effects and seedling age interactions with virus source were not significant. Selection for virus tolerance, based on greenhouse vigor, petiole length or leaflet width measurements, increased the frequency of seedlings subsequently classified as virus-tolerant in the field in both 80- and 101-day-old seedlings. Selection based on greenhouse vigor or petiole length increased the frequency in 129-day-old seedlings. No greenhouse selection method evaluated was effective in 157-day-old seedlings.

Open Access

Open-pollinated progeny from 20 papaya (Carica papaya) cultivars, 2 Carica pubescens and 1 C. goudotiana were evaluated for vegetative growth and for tolerance to papaya ringspot virus under greenhouse and field condition. The artificial inoculation with the viral strain of severe mottle and necrosis symptom type was followed two months after germination. The survival rate and symptom development were significant difference among genotypes. Plant height was negatively correlated with viral survival rate; r =0.58** at greenhouse, and r =0.56** in the field, respectively. The direct ELISA(the conjugate of purified McAb-14 with alkaline phosphatase) was applied to guarantee successful inoculation and to detect plant responding to viral infection one month after artificial inoculation. Then, selection for resistance to papaya ringspot virus is done on a single plant basis. The progeny of positive index of direct ELISA with no symptom development had often from the parent with higher survival rate.

Free access

determine various factors associated with IYSV symptom development such as virus titer and heat stress. This study was undertaken to screen New Mexico onion entries for tolerance to IYSV infection and of symptom expression and correlate the enzyme

Free access

Twenty-six cultivars and two numbered selections of Cucurbita pepo L. pumpkin and four cultivars of C. maxima Duchesne pumpkin were evaluated in field experiments in 1996 and 1997 in Charleston, S.C. The four C. maxima cultivars (`Mammoth Gold', `Big Max', `Rouge Vif d'Etamps', and `Lumina') and three C. pepo cultigens (HMX 6686, HMX 6688, and Magic Lantern) had lower powdery mildew [Sphaerotheca fuliginea (Schlechtend.:Fr.) Pollacci] severities than did the other C. pepo cultivars. Overall, C. maxima cultivars also had less foliage showing virus symptoms and less downy mildew [Pseudoperonospora cubensis (Berk.& M.A. Curtis) Rostovzev] than did C. pepo cultigens. Mid- and long-season cultigens of both species (≥100 days to maturity) produced a greater number of marketable-quality fruit than did short-season cultigens. Cucurbita maxima and C. pepo produced similar numbers of marketable fruit; however, more potential marketable yield was possible in C. maxima since most fruit were affected by virus. The C. pepo cultigens Spookie, HMX 6686, and Spooktacular produced the greatest numbers of marketable fruit. In general, no cultigens were well-adapted to the growing conditions of the humid coastal plain of the southeastern United States.

Free access

Yellow squash (Cucurbita pepo L.) planted after early spring in Mississippi have a strong likelihood of developing green streaks and blotches on the fruit-symptoms of watermelon mosaic virus strain 2. Cultivars with the relatively new precocious yellow gene (PYG) tend to show such symptoms less prominently, and in some cases not at all, when infected. Field trials were conducted at two locations to evaluate several PYG cultivars and compare their WMV-2 symptoms to those of standard, non-PYG types. In both cases, the PYG cultivars had fewer unmarketable fruit due to WMV-2 symptoms, although they were not entirely immune to the virus.

Full access

., 2008 ). The objective of this study was to evaluate Cucurbita germplasm for resistance or tolerance to whiteflies and whitefly-transmitted viruses (CuLCrV and CYSDV) in Georgia and Florida. The genotypes identified have the potential to be used as

Open Access