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  • Author or Editor: Gregg Nuessly x
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Damage due to leaf mining by Liriomyza trifolii (Burgess) is a major problem in many leafy vegetables, especially lettuce. A hierarchy of feeding preference of leafminer on lettuce, Lactuca sativa L. cultivars 'Valmaine', `Parris Island Cos', `Floricos 83', and `Tall Guzmaine' was determined. Leafminers were given a choice of two plants. Observations on the number of times that leafminers probed the leaf surface to feed or oviposit in each plant was counted. `Tall Guzmaine' was significantly preferred in all combinations. Probe ratio of `Tall Guzmaine' verses the other cos lines ranged from 4:1 to 90:1. There were no significant difference between the other three lines, although `Valmaine' had the lowest count in most cases. Based on the pedigrees of the cultivars tested, the observed preferences appears to be under genetic control.

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Host plant resistance is a key element in a viable integrated pest management plan. Resistance to plant feeding was observed on Valmaine cos lettuce, Lactuca sativa L. to the banded cucumber beetle (BCB), Diabotica balteata (LeConte). In no-choice feeding evaluations, adult BCB contained on three week old Valmaine plants gained less weight, died and fed less than individuals contained on susceptible Tall Guzmaine cos lettuce. Individual female BCB held on Valmaine plants also did not have egg development as in those individual held on Tall Guzmaine. Based on weight gain and feeding damage F1, F2, and F3 segregation data indicates that the resistance factor is recessive in inheritance and controlled by more that one gene.

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Bacterial leaf spot (BLS) disease, caused by Xanthomonas campestris pv. vitians (Xcv) has become an increasingly damaging disease in the lettuce production areas of the United States. To understand the nature of the outbreaks of this disease, the pathogenic variations for causing disease were evaluated on 29 lettuce cultivars and germplasm lines using three Xcv isolates recovered in different years from the Everglades Agriculture Area (EAA) of Florida. Significant differences were shown in both the BLS incidences and disease severities among the three Xcv isolates, and the rank from high virulence to less severity was L7 > JF196 > NF1. Our results suggest that the pathogenic variations of the isolates may have been associated with the epidemic outbreaks of BLS in EAA. Among the 29 lettuce genotypes, the host plant resistance was characterized by specific host genotype and Xcv isolate interactions. The leaf lettuce PI358001-1 was consistently in the high resistant category to all three Xcv isolates, and is a promising resistant source for development of resistant cultivars.

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