Evaluation of bell pepper germplasm for Phytophthora blight resistance.

Summary

Phytophthora blight is a serious new disease affecting bell pepper production in Georgia that is very difficult to control. As a first step towards the production of new phytophthora resistant pepper cultivars we screened several thousand pepper lines to find new genetic sources of resistance.

Situation

Phytophthora blight, caused by Phytophthora capsici, is becoming a major disease constraint to bell pepper production in Georgia, where the total farm gate value of bell pepper was $100 million in the year 2007. Phytophthora blight affects multiple plant parts such as the roots, leaves, stems and fruits. Depending upon which organ is affected, phytophthora blight can cause defoliation, stem girdling, or collapse of the plant from root loss. Phytophthora infection is enhanced by warm temperatures and frequent rainfall, conditions that are common in the southeastern U.S. during the summer months. The host range of P. capsici includes multiple crops and weed species, and the oospores can persist in the soil for long periods. Hence, crop rotation with other major crops is often not an effective option to manage P. capsici. Chemical control is based primarily on mefenoxam, and the presence of mefenoxam-resistant strains of the pathogen in commercial fields is a major constraint to the long-term effectiveness of this chemical. The use of P. capsici-resistant bell pepper cultivars is an important aspect in the management of this disease. Resistant cultivars represent the most environmentally friendly and economically sound method of control. Unfortunately, the level of resistance in commercial bell pepper cultivars is not effective in managing these disease syndromes in moist and humid conditions, and new sources of resistance are needed.

Response

A breeding program to develop new P. capsici-resistant bell pepper cultivars is needed. As a first step in this program, new sources of resistance need to be identified. We did this by screening over two thousand pepper accessions (an accession is a pepper line, it can be a cultivar, a grower variety, or even a wild plant) from the USDA pepper collection housed in Griffin, Ga. Nearly all of these accessions have never been tested for Phytophthora resistance. We tested accessions in the greenhouse using several Georgia isolates of Phytophthora capsici, and then validated these tests with field tests.

Impact

A mixture of six Georgia isolates of P. capsici were used for greenhouse mass screening of 2,301 accessions of Capsicum annuum. From the initial screening, 77 accessions were identified as resistant to P. capsici induced root rot. From those 77 accessions, 28 accessions with at least three surviving plants were selected for seed increase and further replicated root inoculation tests. Replicated tests confirmed the resistance of 14 of the 28 accessions, although genetic variability within the accessions hampered the analysis of resistance in some accessions. Ten root rot resistant lines were also tested for resistance to stem rot and leaf blight, and were found to also be highly resistant to these forms of the disease. It appears that single resistant sources can be utilized to breed for resistance to all three forms of the disease, but it is not known if resistance to each form is inherited independently. Two accessions, PI 210237 and PI 640532, demonstrated consistently high levels of resistance to root rot. These two accessions are potential sources of resistance genes that can be incorporated into commercial bell pepper cultivars.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2009
• Geographic Scope: State
• County: Tift
• Program Areas:
  • Agriculture & Natural Resources