Tolerance to Rust (Puccinia allii) in Seed Derived Garlic Progenies

Abstract

In California, rust (Puccinia allii) on garlic (Allium sativum) was not considered an economic problem until 1998, when a severe infection of the disease caused an average 51% reduction in yield throughout the state. The weight of harvested bulbs was 25% to 60% smaller than the average weight in the previous year, and soluble solids were reduced by an average of 15%. Until recently, garlic varieties that are resistant or highly tolerant to rust have not been grown in garlic production fields in California. Open pollinated progenies derived from 3 Plant Introduction accessions of the U.S. Dept. of Agriculture-Agricultural Research Service germplasm collection (PI 493099, PI 540315 and W6 12820) were inoculated with a suspension of urediniospores (1, 2 × 105/mL) isolated from rust infected garlic leaves obtained from production fields in Kings, Fresno and Yolo counties. Inoculations were carried out in a replicated experiment in the field under plastic covers, where 12 hours of misting was applied. The disease symptoms were scored on all leaves of the inoculated plants. The size of observed lesions varied from <1 to 280 mm2. Of the 118 plants evaluated, 9.3% had an average leaf area with rust symptoms of less than 1%. The majority of the plants (83.1%) had 1 to 5% of leaf area infected, and over 6% of plants had symptoms on 5 to 25% of their leaf surface. The highest number of plants with a low percent of rust symptoms on leaves was observed on progenies produced from PI 493099. While all maternal plants used to produce the seeds showed rust symptoms, the presence of progenies with ≤0.5% of leaf area infected indicated that a tolerance source to P. allii may exist in the A. sativum NPGS, germplasm collection.