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John Klingler, Irina Kovalski, Leah Silberstein, Gary A. Thompson, and Rafael Perl-Treves

Resistance to cotton-melon aphid (Aphis gossypii Glover) segregated as a single dominant gene in a melon (Cucumis melo L.) mapping population derived from the cross `Top Mark' × PI 414723. Sixty-four F2-derived F3 families were used to map the aphid resistance locus, Vat, with respect to randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers. RFLP markers NBS-2 and AC-39 flanked Vat at distances of 3.1 cM and 6.4 cM, respectively. NBS-2 is homologous to the nucleotide binding site-leucine-rich repeat (NBS-LRR) superfamily of plant resistance genes. Another homolog of this superfamily, NBS-5, was positioned ≈16.8 cM from Vat, raising the possibility that Vat resides in a cluster of NBS-LRR paralogs. RFLP marker AC-8, which has similarity to plant lipoxygenases, was positioned at ≈5.5 cM from Vat. Monogenic resistance to A. gossypii has been identified in two sources of melon germplasm, Indian accession PI 371795 (progenitor of PI 414723) and Korean accession PI 161375. To test for an allelic relation between the genes controlling aphid resistance in these two distinct germplasm sources, melon plants of a backcross population from a cross between two resistant lines having Indian- or Korean-derived resistance were infested with aphids. At least 90 out of 92 segregating progeny were aphid resistant, suggesting that the same resistance gene, Vat, is present in both sources of melon germplasm.

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J.K. Collins, P. Perkins-Veazie, N. Maness, and B. Cartwright

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Albert N. Kishaba, Steven J. Castle, Donald L. Coudriet, James D. McCreight, and G. Weston Bohn

The spread of watermelon mosaic virus by the melon aphid (Aphis gossypii Glover) was 31%, 74%, and 71% less to a melon aphid-resistant muskmelon (Cucumis melo L.) breeding line than to the susceptible recurrent parent in a field cage study. Aphid-resistant and susceptible plants served equally well as the virus source. The highest rate of infection (97.9%) was noted when target plants were all melon-aphid susceptible, least (26.7%) when the target plants were all melon-aphid resistant, and intermediate (69.4%) when the target plants were an equal mix of aphid-resistant and susceptible plants. The number of viruliferous aphids per plant required to cause a 50% infection varied from five to 20 on susceptible controls and from 60 to possibly more than 400 on a range of melon aphid-resistant populations. An F family from a cross of the melon aphid-resistant AR Topmark (AR TM) with the susceptible `PMR 45' had significantly less resistance to virus transmission than AR TM. Breeding line AR 5 (an aphid-resistant population with `PMR 5' as the recurrent parent) had significantly greater resistance to transmission than other aphid-resistant populations.

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J.R. Fisher and S.G.P. Nameth

Melon aphids were provided by Karen Magnuson and Celeste Welty, Dept. of Entomology, The Ohio State Univ., Columbus. `Peto 696' tomato seedlings were provided by R.M. Riedel, Dept. of Plant Pathology, The Ohio State Univ., Columbus. Lypholized

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Wenhua Lu, J.V. Edelson, Jim A. Duthie, and B. Warren Roberts

Factors of crop management such as irrigation, cultivation, cultivar selection, and control of insect pests and plant diseases play important roles in watermelon production. To gain a better understanding of how intensity of crop management affects yield, we conducted a comparative study contrasting high and low intensity management in 1997, 1999, and 2000. High-intensity management (HM) included the use of trickle irrigation, black plastic mulch, insecticides, and fungicides, not used under low-intensity management (LM). We examined the effects of management intensity on watermelon productivity, the variation in such effects among watermelon cultivars, and the mediating effect of survival of watermelon plants, abundance of insect pests, and incidence of anthracnose (% leaves with anthracnose lesions). The results indicated that HM produced 100% greater marketable fruit yield per area and marketable fraction of total fruit than LM in 2 out of 3 years. The effect of management intensity on plant survival was related to this effect on yield in 1 out of 2 years, and contributed to the latter by increasing weight and number of marketable fruit per plant under HM. We detected no significant effect of abundance of insect pests and incidence of anthracnose on yield. There was variation in the effect of management intensity on yield among watermelon cultivars in 1 out of 3 years. The triploid `Gem Dandy' showed great differences in yield between HM and LM in 2 years, producing on average 28.9 Mg·ha-1 of marketable fruit yield under HM compared to 14.0 Mg·ha-1 under LM. `Gem Dandy' also produced 100% higher yield of marketable fruit per area, per plant, and marketable fraction of total fruit than the open-pollinated diploid `Allsweet' or the diploid hybrid `Sangria.' Each year during the 3-year study, all three cultivars had a similar density of insect pests, incidence of anthracnose, and plant survival after transplant and at harvest. This study provided information on the collective impact of multiple aspects of watermelon management on yield.

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Fred T. Davies Jr., Chunajiu He, Amanda Chau, Kevin M. Heinz, and Andrew D. Cartmill

This research details the influence of fertility on plant growth, photosynthesis, ethylene evolution and herbivore abundance of chrysanthemum (Dendranthema grandiflora Tzvelev `Charm') inoculated with cotton aphids (Aphis gossypii Glover). We tested five fertility levels that consisted of 0%, 5%, 10%, 20%, and 100% (375 ppm N) of recommended nitrogen levels. Aphid abundance was greatest at high fertility. Fertility affected the vertical distribution of aphids. A higher population of aphids were observed in physiologically mature and older leaves at low fertility, whereas at high fertility young leaves had 33% more aphids than older, basal leaves. Aphids depressed plant vegetative and reproductive growth, and altered carbohydrate partitioning at high fertility. Aphid-inoculated (AI) plants at high fertility had increased specific leaf area [(SLA), i.e., thinner leaves] and greater leaf area than aphid-free (NonAI) plants. Aphids caused greater ethylene production in reproductive buds and young leaves of high fertility plants, but had no effect on ethylene evolution in physiologically mature or older, basal leaves. Plant growth, leaf nitrogen (N), phosphorus (P), iron (Fe) and manganese (Mn) increased at higher fertility, as did chlorophyll and photosynthetic rates. Leaf N was highest in young and physiologically mature leaves compared to basal leaves. Aphids decreased leaf N and P. Aphids reduced photosynthesis in young leaves of high fertility plants, whereas physiologically mature and older leaves were unaffected.

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P.M. Perkins-Veazie, J.K. Collins, N. Maness, and B. Cartwright

High populations of melon aphid (aphis gossypii) reduce cantaloupe plant growth and yield; effects on subsequent fruit quality are unknown. The purpose of this study was to evaluate fruit quality from plants with high and low aphid populations. Up to 50% of melons from plants having high aphid populations were unmarketable due to surface sooty mold. Melons from plants with high or low aphid populations, but not cultivars, were similar in flesh quality. The internal color of `Perlita' and `Sweet Surprise' was a more yellow hue while that of `TAM Uvalde' was more orange. `Sweet Surprise' melons were lower in percent soluble solids concentration and titratable acidity, but were higher in mg fructose/ml juice compared to the other cultivars. A trained taste panel of 30 people evaluated melons from 2 cultivars showing little damage from melon aphid infestations and from 2 cultivars exhibiting high damage. All melons had similar taste qualities with acceptable sweetness, flavor, odor and texture. These results show that high aphid populations deleteriously affect cosmetic appearance, but not flesh quality, of melons.

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James D. McCreight

PI 414723 has received much attention from melon (Cucumis melo L.) breeders, pathologists, and entomologists for resistances to zucchini yellow mosaic and watermelon mosaic viruses, including resistances to virus multiplication and subsequent transmission by the melon aphid, powdery mildew resistance, and melon aphid (Aphis gossypii Glover). PI 414723 was derived from PI 371795, which was a contaminant in cucumber (Cucumis sativus L.) PI 175111 collected in 1948 by Walter N. Koelz in Mussoorie, Uttar Pradesh, India (altitude 1829 m). Its fruit, which have soft flesh and rind that split at maturity, are used in soups and stews, and the seeds are roasted and eaten. PI 414723, PI 371795, and the related Ames 20219 and progeny 92528a were resistant to California and Florida isolates of papaya ringspot virus watermelon strain (PRSV-W). Plants were either symptomless, or they exhibited local lesions, systemic necrosis, or systemic spots. Resistance to PRSV-W is conditioned by a single dominant gene. Allelism with Prv1 (PI 180280, Rajkot, Gujarat, India), Prv2 (PI 180283, Bhavnagar, Gujarat, India), Nm (`Vedrantais, Fance), and a recently described gene for PRSV-W resistance in PI 124112 (Calcutta, India) is yet to be determined.

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J.L. Shipp and Yun Zhang

Application of entomopathogenic fungi by inundative releases has been attempted for control of a wide range of insect pests, with generally poor results. This is largely because entomopathogens are often treated as direct substitutes for chemical insecticides and applied without an adequate knowledge of their interactions with the local environment. Humidity of greater than 90% RH has long been regarded as the a critical condition for germination and infection by the spores. With both temperature and humidity controlled, greenhouse crops offer an excellent potential for pest control using entomopathogens. The long-term maintenance of >90% RH, however, is not standard practice in greenhouse production. This study explored the possibility of improving the efficacy of the fungi by temporarily changing greenhouse humidity without adversely affecting crop growth. The study included laboratory and greenhouse trials. In laboratory trials, four humidity levels of 75%, 80%, 89%, and 97.5% RH were evaluated over a 48-h period. Three commercial products of Beauveria bassiana were evaluated (Naturalis-O, Botanigard 22 WP, and Botanigard ES). Greenhouse pests of green peach aphid, melon aphid, western flower thrips, whitefly, and two-spotted spider mite were used as target insects. The infection rate of B. bassiana was found to increase when the sprayed adult insects were exposed to higher humidity levels with the maximum infection obtained at 97.5% RH. Percent infection and difference between humidity levels, however, were formulation- and host-dependent. The highest overall control efficacy was obtained by using Botanigard ES. Botanigard ES was highly effective to adult green peach aphid, melon aphid, and greenhouse whitefly at high humidities. Effects of B. bassiana against biological control agents for greenhouse vegetable crops were also evaluated. Greenhouse trials were conducted in two adjacent greenhouse compartment with high and low humidity conditions for 48 h, respectively, for selected pest insects to valid laboratory results.

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U.K. Schuch, J.A. Bethke, and R.A. Redak

Water stress and N fertilization can have a profound effect on populations of phytophagous insects. While species and cultivar selection can identify plants that are resistant to common insect pests, cultural practices may further decrease the susceptibility to insect attacks. Six poinsettia and six chrysanthemum cultivars were grown under well-watered or water-deficient conditions, and three fertilizer regimes with low, medium, or high concentrations of N. Vegetative plant growth and longevity and fecundity of various insect pests on these plants were determined. Host plant suitability to insects was estimated by the quantity of foliar soluble protein. Low irrigation reduced leaf area and leaf and stem dry weights 36% to 41% in poinsettias and 26% to 28% in chrysanthemum. Leaf area and leaf dry weight increased linearly in response to increasing fertilizer concentrations in poinsettia and chrysanthemum. Cultivar-specific differences were found for all variables of vegetative growth in poinsettiasand chrysanthemum. Cultivar also strongly affected insect preference, development, and fecundity. Low irrigation significantly reduced insect survivorship of the silverleaf whitefly on poinsettias. On chrysanthemum, leafminers, thrips, and melon aphids were unaffected by irrigation or fertilizer treatments. Chrysanthemum cultivar choice strongly affected the number of insects or development time.