COMPARISON OF BLACKLINE RESISTANT AND CONVENTIONAL ENGLISH WALNUT VARIETIES

Blackline disease resistance is a desirable characteristic for walnut orchards in the Central Coast and northern San Joaquin Valley regions of California where this disease has been the most prevalent. A number of blackline resistant varieties from the UC Davis breeding program have been evaluated in the Central Coast for several years. In a number of characteristics such as average nut weight, percent edible yield, percent light and extra-light kernels, reflected light index and relative value, there are blackline resistant varieties that compare favorably to conventional varieties. The blackline resistant variety 93-045-1 is comparable in most parameters except nut size. The blackline resistant variety 94-022-24 fails only in yield. Blackline resistant varieties currently being tested in the field are close to being commercially acceptable and it is hoped that the breeding program will shortly have fully acceptable varieties available. For conventional varieties, ‘Gillet’, ‘Bonturi’ (64-57) and ‘Tulare’ looked most promising. OBJECTIVES Blackline disease caused by the cherry leafroll virus (CLRV) has been a serious disease of California walnut trees particularly in the Central Coast and in the northern San Joaquin Valley. Varieties resistant to blackline disease have been developed by the UC Davis walnut breeding program. All of these are numbered selections that have not been released for propagation or sale. Some of these selections have been tested in San Benito County under test agreements. This report will summarize five years of crackout analyses of blackline resistant and conventional walnut varieties for various quality parameters. SIGNIFICANT FINDINGS