The watermelon (Citrullus lanatus var. lanatus) ‘AU-Performance’ was developed for resistance to multiple fungal pathogens and the plant virus, zucchini yellow mosaic virus (ZYMV). A greenhouse-based evaluation was carried out to determine the response of ‘AU-Performance’ to inoculation with three important cucurbit (Cucurbitaceae) viruses in the genus Potyvirus: papaya ringspot virus (PRSV), watermelon mosaic virus (WMV), and ZYMV. The evaluation included the resistant parent (PI595203), the susceptible parent (‘AU-Producer’), and varieties AU-Allsweet and Charleston Gray. Each of the three viruses systemically infected ‘AU-Performance’ with 100% infection and development of characteristic systemic symptoms. The susceptible parent (‘AU-Producer’), ‘AU-Allsweet’, and ‘Charleston Gray’ responded similarly with 100% infection and systemic symptoms. In contrast, the resistant parent (PI595203) was resistant to WMV and ZYMV; however, PRSV-inoculated plants developed a systemic infection with accompanied symptoms and high levels of PRSV accumulation in noninoculated leaves. PI595203 was shown in previous studies to be resistant to PRSV. We show in this report that under greenhouse conditions and application of virus by mechanical inoculation, ‘AU-Performance’ was not resistant to infection by the three potyviruses.
John F. Murphy and Fenny Dane
John F. Murphy, Edward J. Sikora, Bernard Sammons, and Wojciech K. Kaniewski
Three processing tomato (Lycopersicon esculentum Mill.) lines engineered to express the cucumber mosaic virus (CMV) capsid protein (CP) gene were evaluated in the summers of 1995 and 1996 under high levels of naturally occurring CMV disease pressure. One tomato line expressed the capsid protein gene from a subgroup II isolate of CMV (line 11527), whereas two lines (12261 and 12295) expressed the capsid protein genes from a CMV subgroup I and a subgroup II isolate. Evaluation of CMV incidence based on symptomatic plants revealed that only 9% and 8% of the plants in line 11527 were infected in 1995 and 1996, respectively, 5 weeks after being transplanted. None of the plants in line 12261 developed symptoms in 1995, whereas 26% were symptomatic in 1996. There were no symptomatic plants in line 12295 in either the 1995 or the 1996 trial. In contrast to the CMV transgenic lines, 96% and 95% of the susceptible control plants were symptomatic by the 5-week rating period. CMV incidence in the CMV transgenic lines was much higher when infection was based on detection of virus by enzyme-linked immunosorbent assay (ELISA). This was particularly true in the 1996 trial where no less than 97% of the plants within a treatment were determined to be infected. Though a relatively high percentage of the transgenic plants were infected, the amount of CMV that accumulated in these plants was significantly less than in the susceptible controls, which may explain the occurrence of the attenuated symptoms. Despite CMV infection of the transgenic lines in the Alabama field trials, the performance of these lines could be of practical value to growers.
Joseph W. Kloepper, M.S. Reddy, Choon-min Ryu, and John F. Murphy
Use of beneficial rhizobacteria to enhance growth and induce systemic disease protection in transplants. Plant associated bacteria have been studied for the capacity to provide plant growth enhancement and biological disease control. “Rhizobacteria” are bacteria from the rhizosphere that have the capacity to colonize plant roots following introduction onto seeds or into soil. Effects of rhizobacteria on plants may be deleterious, neutral, or beneficial. Beneficial rhizobacteria are termed “PGPR—plant growth-promoting rhizobacteria.” In developmental studies aimed at reducing to practice the concept of induced systemic disease protection mediated by PGPR, we discovered that mixtures of PGPR and an organic amendment into the soilless media used to prepare tomato transplants resulted in highly significant and reproducible plant growth promotion. Time for development of transplants was typically reduced from 6 weeks for controls receiving industry standard fertility and growth regimes to 4 weeks for seedlings grown in soilless mix into which the PGPR had been incorporated. This marked growth promotion was also associated with systemic protection against pathogens. When transplants were inoculated with the tomato spot pathogen, significantly fewer lesions developed on plants grown in the biological system than on control plants. Similar effects on plant growth and systemic disease protection were seen with cucumber, bell pepper, and tobacco, suggesting that the benefits are not highly crop or cultivar specific. Results of recent field studies will be presented. We conclude that incorporation of PGPR into soilless mixes is a technologically useful and feasible way to deliver benefits to transplants.
Joseph. M. Kemble, Goeff W. Zehnder, W. Robert Goodman, Mahefatiana Andrianifahanana, Ellen M. Bauske, Edward J. Sikora, and John F. Murphy
The Alabama Tomato Integrated Pest Management (IPM) Program was demonstrated during two growing seasons in southeastern Alabama. The program consisted of a twice-a-week insect/disease scouting service combined with a weather-timed spray program (TOM-CAST). On average, growers made four fewer insecticide applications and three to four fewer fungicide applications when following the IPM program compared to their conventional, calendar-based program. There was no apparent reduction in yield when following the IPM program. An economic analysis indicated that growers following the IPM program saved an average of $54.36/acre ($134.32/ha).