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Zhengke Zhang, Zhaoyin Gao, Min Li, Meijiao Hu, Hui Gao, Dongping Yang, and Bo Yang

excess of the scavenging capacity, which causes membrane spoilage and consequently results in CI in mango fruit ( Ding et al., 2007 ; Wang et al., 2008 ; Zhou et al., 2006 ). Postharvest heat treatments have been used to reduce the development of CI

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Nathan J. Jahnke, John M. Dole, and H. David Shew

Botrytis diseases. Plant materials shipped wet and with spores are likely to develop lesions within 2 d. Fluctuating air temperatures during transit may not affect disease development, but they can cause leaf yellowing, which could lead to disease during

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E.M. Lamb, R.M Sonoda, E.F. Oxman, and E.N. Rosskopf

Hydroponic greenhouse production of sweet peppers is a well-established and growing industry in South Florida. Plants are in the greenhouse from about October until June, and the long season makes disease problems particularly costly to producers. A stem rot caused by Fusarium solani (anamorph of Nectria haematococca) and previously unreported in South Florida was found on greenhouse peppers in March 1999. Black lesions occurred at nodes where the plant was pruned or fruit was harvested. Tissues above the lesion appeared normal until the lesion girdled the stem, at which point the tissues above the lesion wilted and died. Greenhouse surveys over a 4-month period suggested that environmental factors played a role in number of infected plants and lesion size. A controlled environment chamber test was conducted to evaluate the effect of temperature and cultivar on disease development and severity. Three greenhouse pepper cultivars; Cubico, Triple 4, and Kelvin, were stem inoculated with F. solani at the 3- to 4-week stage. Noninoculated plants were included as a control. Fifteen plants of each cultivar plus control plants were incubated at ≈35, 32, and 29 °C for 2 weeks. The test was run twice. All inoculated plants developed lesions while no control plants developed disease symptoms. Lesion length and diameter were measured for all plants and wilting associated with disease development was noted. Temperature had a significant effect on disease severity with larger lesions and more frequent wilting occurring at higher temperatures. Cultivar did not affect the development of the disease.

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Chen Chen, Meng-Ke Zhang, Kang-Di Hu, Ke-Ke Sun, Yan-Hong Li, Lan-Ying Hu, Xiao-Yan Chen, Ying Yang, Feng Yang, Jun Tang, He-Ping Liu, and Hua Zhang

., 2002 ). The deletion of bcsod1 in the necrotrophic fungal pathogen Botrytis cinerea causes smaller lesion on pea ( Pisum sativum ) leaves, which proves that this gene is essential for full virulence of B. cinerea on plants ( Rolke et al., 2004

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Gustavo Gimenez, James R. Ballington, and Robert D. Milholland

Two experiments were designed to study components of resistance to Colletotrichum acutatum on runners of three strawberry cultivars: incubation period, latent period, length of the lesion and spore production, and infection frequency with three levels of inoculum density (104, 105, 106 spores/cc) were considered. Rate of disease development was also determined. There were significant differences in all the components among the resistant and susceptible cultivars. Both 'Chandler' and 'Sweet Charlie' expressed susceptible reactions. The length of the lesion, number of spores/cm of the lesion, incubation period, latent period, and rate of anthracnose development were statistically similar in 'Chandler' and 'Sweet Charlie'. The only significant difference among them was found in infection frequency. 'Chandler' had a greater number of infection sites with all three concentrations of spores included. The cultivar Pelican showed a high level of partial resistance associated with longer incubation and latent periods, lower number of spores/cm of lesion, shorter lesion, smaller number of infection sites, and lower rate of disease development.

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William S. Bramlage

On Granny Smith apples, scald development exhibits characteristics that are typical of chilling injury. Yet, when `Cortland' and `Delicious' apples were placed in loosely closed polyethylene bags and kept continuously at 20C, scald-like injuries began to occur after 2 weeks. Lesions were predominantly expressed as lenticel spotting and as bronzing in the calyx cavity, which are not typical of superficial scald, but some typical scald lesions did develop on the shaded sides of the fruit. Lesion development decreased with later harvest of fruit. Fruit enclosed in poly bags accumulated high concentrations of α-famesene and conjugated trienes in their peel. Whether or not scald should be considered to be a chilling injury will be examined in light of these contrasting results.

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D.S. Achor, L.G. Albrigo, and C.W. McCoy

Upper surface leaf lesions on `Sunburst' mandarin [(Citrus reticulata Blanco × (C. paradisi Macf. × C. reticulate)] associated with feeding by the citrus rust mite [Phyllocoptruta oleivora (Ashm.)] are more severe than those on other citrus cultivars. Development of leaf lesions on `Sunburst' mandarin and two other cultivars were examined by light and electron microscopy. Damaged leaves treated with a fungicide confirmed that the anatomical changes on `Sunburst' are an enhanced wound periderm response to feeding injury by rust mite and not the result of fungal invasion.

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B.M. Pryor, R.M. Davis, and R.L. Gilbertson

The susceptibility of 46 carrot cultivars to infection by Alternaria radicina Meier, Drechsler, and Eddy, causal agent of black rot disease, was evaluated in field trials with a toothpick inoculation method. Toothpicks infested with A. radicina were inserted into the shoulders of 10- to 12-week-old carrots (Daucus carota L.) and lesion areas were measured 9 to 10 weeks later. There were significant differences in lesion size among cultivars. Relatively resistant cultivars included `Panther' and `Caro-pak', and susceptible cultivars included `Royal Chantenay' and `Nogales'. Nine of the cultivars were inoculated with A. radicina-infested toothpicks and maintained in cold-storage for 10 weeks. Lesion development was greater in cold-storage than in the field, but the relative ranking of cultivars in terms of resistance to A. radicina was similar.

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Swee-Suak Ko, Jenn-Wen Huang, Jaw-Fen Wang, Subramanyam Shanmugasundaram, and Woo-Nang Chang

Assistant specialist. Professor. Associate plant pathologist. Plant breeder. Professor. Journal paper no. 171 of the Asian Vegetable Research and Development Center. The authors are grateful to the Genetic Resource and Seed Unit at AVRDC, for the

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Cristina Mallor, José María Álvarez, and Marisol Luis-Arteaga

Melon necrotic spot virus (MNSV) has been found affecting melon (Cucumis melo L.) crops. At present the only known resistance in melon is controlled by a single recessive gene, nsv. The presence of nsv in a melon genotype has been correlated with the lack of necrotic lesions on the mechanically inoculated cotyledons. Thus, in a screening program for MNSV resistance, melon genotypes that developed necrotic lesions in the inoculated cotyledons were discarded. However, in this paper we show that some melon accessions mechanically inoculated with MNSV do develop local necrotic lesions, therefore showing the absence of the gene nsv, but fail to develop the systemic symptoms typical of diseased plants under the screening conditions. In some of these accessions the influence of the temperature on the development of systemic symptoms was studied. The results showed that, depending on the accession, temperatures under 25 or 20 °C enhanced the systemic development of the disease. One of the tested varieties, `Doublon', did not develop systemic symptom at any of the tested temperatures (15, 17.5, 20, 22.5, 25, 27.5, and 30 °C). In this variety, the lack of systemic symptoms was correlated to the lack of virus infection of these tissues based upon ELISA results. MNSV was not detected in the uninoculated parts of the plant, and seems to remain confined to the local lesions produced on the cotyledons following the mechanical inoculation. Restriction of viral multiplication and/or cell-to-cell movement could explain the pattern of viral distribution in this variety. This reaction was observed in the `Doublon' plants mechanically inoculated with each of five isolates of MNSV tested, including an isolate that overcomes the nsv gene resistance.