Factors Influencing the Infection of Cultivated Grape (<i>Vitis</i> spp. Section <i>Euvitis</i>) Shoot Tissue by <i>Guignardia bidwellii</i> (Ellis) Viala & Ravaz
Open Access
- Author:
- Northover, Philip Robert
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 16, 2007
- Committee Members:
- James Warren Travis, Committee Chair/Co-Chair
Robert Michael Crassweller, Committee Member
Erick D De Wolf, Committee Member
Elwin Lynn Stewart, Committee Member
Wakar Uddin, Committee Member - Keywords:
- infection requirements
plant pathology
Phyllosticta
cultivar
surface wetness
shoot tissue
Guignardia bidwellii
temperature
grape diseases
black rot
pycnidia
conidiospores
fungi
ascomycete
Vitis - Abstract:
- <i>Guignardia bidwellii</i> (Ellis) Viala & Ravaz (anamorph <i>Phyllosticta ampelicida</i> (Englem.) van der Aa) is the cause of black rot of grape, a destructive disease that has caused significant losses to grape (Vitis spp.) production, in the northeastern United States on the subgenus <i>Euvitis</i> (<i>Vitis vinifera</i> L., <i>V. labrusca</i> L. and <i>Vitis</i> interspecific hybrids). All expanding green tissue is susceptible. The influence of inoculum concentration, wetness duration and temperature at inoculation, cultivar, relative humidity, and daily internode expansion, were evaluated under controlled conditions. Consistent development of black rot shoot symptoms by artificial methods has been difficult. A small humidity chamber was developed that promoted shoot infection and symptom development. Application of conidia at concentrations of 1x104 and 1x105 spores/ml promoted significantly (p<0.05) greater disease severity. Pycnidium production was significantly higher at an inoculum concentration of 1x105 spores/ml on <i>Vitis</i> shoots, regression analysis of the instantaneous growth rate calculated from daily internode measurements (GRI) immediately after inoculation was significant (p=0.0350, R2=0.026) for the square root (SQRT) of pycnidia density (PD-- pycnidia/cm2) but not for symptom severity (DS) in the absence of the concentration terms in the analysis. The effects of temperature and surface wetness duration on the development of black rot of grape shoots by G. bidwellii conidiospores was evaluated on three cultivars, Niagara¯ (<i>V. labrusca</i>),Chardonnay (<i>V. vinifera</i>) and Aurore (<i>V. labrusca</i> x <i>V. vinifera</i>). Plants were inoculated at combinations of seven temperature levels (12C to 30C in 3C intervals) and six shoot wetness durations (10 to 30 hours in 5 hour intervals) and evaluated for black rot shoot symptom incidence, DS, and PD. Symptoms did not develop at 12 and 30C at wetness durations less than 15 hours. All other temperature treatments promoted disease development on shoot tissue with wetness durations of 10 hours or greater. Analysis of variance (ANOVA) and regression analyses were used to determine linear, quadratic, or cubic functional relationships between temperature and shoot wetness duration and disease severity (%) and pycnidium density (pycnidia/cm2). Significant terms were incorporated into a regression model to describe the relationship. Square root transformed DS was significantly (p<0.0001) influenced by wetness duration, temperature and the interaction term. The adjusted coefficients of determination (R2) for the polynomial regressions were all low (0.173). Square root transformed pycnidium density was significantly (p<0.05) influenced by cultivar, temperature, and the temperature with wetness interaction. Each cultivar was examined separately due to the significant cultivar response. The response of Aurore and Chardonnay was significantly influenced by temperature. At 24C significantly more pycnidia were produced than at any other temperature. Wetness duration was significant for Niagara, 20 hours of wetness produced a significantly greater number of pycnidia than any other wetness period. A refinement of the infection requirements was conducted on <i>V. vinifera</i> cv. Chardonnay grapes, a minimum of 7.5 hours of shoot wetness at 21C was suitable for infection. Disease severity and pycnidium density increased as leaf wetness increased at a given temperature. DS and PD were both significantly (p<0.0001) influenced by temperature, wetness duration, the average growth rate immediately after inoculation (GRA2) and the wetness-temperature interaction. The growth four to five days after inoculation (GRA5) also significantly influenced shoot DS (p=0.003) and PD (p=0.0005). Two experiments looked at the susceptibility of <i>V. labrusca</i>, <i>V. vinifera</i>, interspecific hybrids, and <i>V. riparia</i> cultivars. Eighteen cultivars were screened for DS and PD from shoot infections by conidia. Cultivar significantly influenced DS and PD (p=0.0001). Individual runs differed in the order of the cultivars, but generally the <i>V. vinifera</i> cultivars, Riesling, Cabernet Sauvignon, and Chardonnay, <i>V.labrusca</i> Niagara, and the interspecific hybrid Aurore were significantly higher in disease severity than the other cultivars (p<0.05). Pycnidium density (PD) was generally highest among the V. vinifera cultivars, the <i>V. labrusca</i> cultivar Niagara and the American hybrid cultivar Cayuga White. <i>V.labrusca</i> cultivar Concord, recognized as susceptible to black rot leaf and fruit infections, was not among the most susceptible cultivars for shoot infections. The influence of post infection relative humidity level (RH) on the development of shoot symptoms after inoculation and subsequent drying of foliage with G. bidwellii conidia was investigated. There was a significant effect of relative humidity treatment for PD (p=0.038) but not for DS (p=0.3840). PD was significantly greater when RH=86.1(sd 3.1%) (High), as opposed to RH=36.7 (sd 12.3%) (Low) for the first five days after inoculation, RH conditions five days after inoculation had no effect on PD. This study is the first investigation into the conditions that can influence black rot symptom severity and pycnidium development on grape shoots.