COMPARISON OF BLACKLINE RESISTANT AND CONVENTIONAL ENGLISH WALNUT VARIETIES

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1 COMPARISON OF BLACKLINE RESISTANT AND CONVENTIONAL ENGLISH WALNUT VARIETIES William W. Coates ABSTRACT 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 is comparable in most parameters except nut size. The blackline resistant variety 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 1. The blackline resistant varieties tested tend to be slightly lighter in weight than conventional varieties although , and were similar in weight to Chandler. 2. Two blackline resistant varieties ( , ) were the equivalent of Serr in percent edible yield and one ( ) surpassed Serr. 3. All blackline resistant varieties were inferior to conventional varieties in percent large, sound nuts. 4. Three blackline resistant varieties ( , , ) were similar to Payne in percent light and extra-light kernels and was superior to all varieties. 5. All conventional varieties averaged an RLI of 52.0 or more as did four blackline resistant varieties ( , , , ). One blackline resistant variety surpassed all other varieties ( ). 6. Relative value varied from 0.84 ( Hartley ) to 1.10 ( Serr ) for conventional varieties and 0.75 ( ) to 1.15 ( ) for blackline resistant varieties. California Walnut Board 55 Walnut Research Reports 2012

2 PROCEDURES Walnut samples were collected at harvest, hulled in the field, placed in mesh bags, labeled and dried in a laboratory drying oven. Samples (1000 g) were submitted to Diamond Foods in Stockton, CA for crackout analyses. These blackline resistant test trees are planted in an existing orchard with blackline-infected conventional varieties. The conventional varieties surveyed were Payne, Serr, Howard, Chandler, Tulare, Hartley, Gillet and Bonturi (64-57). The blackline resistant varieties surveyed were , , , , , , and RESULTS Results of six major quality factors are shown in tables 1 through 6. These are average nut weight (g), percent edible yield, percent large sound nuts, percent extra-light and light colored kernels, reflected light index (RLI) and relative value. For each parameter, a higher value is desirable. Relative value is a measure of overall value and is calculated by the equation: percent edible yield x RLI x conversion factor. For all tables, nr means no record. Average nut weights for the tested blackline resistant and conventional varieties are listed in table 1. Overall, the tested blackline resistant varieties tend to be slightly lighter in weight than conventional varieties although , and were similar in size to Chandler. The heaviest conventional nuts were Bonturi (64-57) and the lightest were Chandler. The heaviest blackline resistant nuts were and the lightest were Percent edible yield results are listed in table 2. Serr was the best conventional variety for percent edible yield and two blackline resistant varieties were comparable ( , ) and one ( ) was superior to Serr (only one year of data). The worst percent edible yield results were Hartley for conventional and for blackline resistant varieties. For percent large sound nuts, all of the blackline resistant varieties were inferior to the conventional varieties except The highest percent large sound nuts for conventional varieties were Gillet and Bonturi (64-57) and for the blackline resistant variety The lowest percent was Chandler for conventional nuts and and for blackline resistant varieties. Three blackline resistant varieties were similar to Payne in the percent of extra-light and light kernels ( , and ) while was superior to all varieties in kernel color. The highest percent for conventional varieties was Gillet and the lowest was Payne. For RLI, all conventional varieties averaged 52.0 or above. Four blackline resistant varieties averaged 52.0 or above ( , , , ). One blackline resistant variety ( ) was superior to all other varieties for RLI. The highest value for RLI in conventional varieties was Bonturi (64-57). The lowest value for conventional varieties was Payne and for blackline resistant varieties was Relative value for conventional varieties varied from 0.84 ( Hartley ) to 1.10 ( Serr ). Blackline resistant varieties varied from 0.75 ( ) to 1.15 ( ) for relative value. California Walnut Board 56 Walnut Research Reports 2012

3 DISCUSSION A number of blackline resistant numbered selections currently being evaluated off-campus appear to come close to being acceptable commercial varieties. The selection has had consistently good yields and has had acceptable kernel weights, color (as measured by both light and extra-light kernels and RLI) and relative value but the nut is small overall. The selection is good or superior in all reported characteristics and, in the field, the tree is vigorous. Unfortunately, it suffers from low yields and appears to be slow to come into bearing although two trees in San Benito County are now producing adequate crops. For conventional varieties, Gillet and Bonturi (64-57) look promising and Tulare was better than Chandler in several characteristics. Tulare also is earlier in harvest than Chandler and appears to have some resistance to walnut anthracnose disease although it is more susceptible to walnut husk fly. Chandler and Howard have been utilized to some extent in the Central Coast as replacements for Payne which has been the variety most impacted by blackline disease but Chandler is very late for harvest date. Despite being superior in several characteristics, Serr is not recommended due to pistillate flower abscission and the inability to time plant growth regulator sprays for this problem adequately with the prolonged bloom period in the Central Coast. The primary merit of this survey is to show that blackline resistant varieties are close to being of commercial acceptance. Some of the current group of potentially blackline resistant selections that are still being tested for resistance on the UC Davis campus appear to be fully equivalent to conventional varieties in quality. California Walnut Board 57 Walnut Research Reports 2012

4 TABLE 1: MEAN NUT WEIGHT (g) Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 9.45 nr Yes nr nr 9.36 nr nr Yes nr nr nr 9.62 nr 9.62 BL Resistant = Blackline resistant (CLRV hypersensitive) TABLE 2: % EDIBLE YIELD Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 53.5 nr Yes nr nr 60.2 nr nr Yes nr nr nr 44.0 nr 44.0 BL Resistant = Blackline resistant (CLRV hypersensitive) California Walnut Board 58 Walnut Research Reports 2012

5 TABLE 3: PERCENT LARGE SOUND NUTS Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 75 nr Yes nr nr 83 nr nr Yes nr nr nr 58 nr 58 BL Resistant = Blackline resistant (CLRV hypersensitive) TABLE 4: PERCENT LIGHT AND EXTRA-LIGHT KERNELS Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 70 nr Yes nr nr 64 nr nr Yes nr nr nr 67 nr 67 BL Resistant = Blackline resistant (CLRV hypersensitive) California Walnut Board 59 Walnut Research Reports 2012

6 TABLE 5: REFLECTED LIGHT INDEX (RLI) Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 50.3 nr Yes nr nr 48.8 nr nr Yes nr nr nr 47.6 nr 47.6 BL Resistant = Blackline resistant (CLRV hypersensitive) TABLE 6: RELATIVE VALUE Payne No Serr No Howard No Chandler No Tulare No Hartley No Gillet No nr Bonturi (64-57) No Yes Yes Yes nr nr nr Yes nr Yes nr nr nr Yes nr nr 0.98 nr Yes nr nr 1.07 nr nr Yes nr nr nr 0.75 nr 0.75 BL Resistant = Blackline resistant (CLRV hypersensitive) California Walnut Board 60 Walnut Research Reports 2012