COMPARISON OF BLACKLINE-RESISTANT AND CONVENTIONAL WALNUT VARIETIES IN THE CENTRAL COAST - 2013 William W. Coates ABSTRACT Samples of nine conventional walnut varieties were compared to samples of nine blacklineresistant varieties from the UC Davis Walnut Improvement Program for several walnut quality parameters including mean nut weight, percent large sound nuts, percent edible yield, reflected light index and relative value. Overall, the highest value walnuts as measured by relative value were two samples of Serr, and one each of 94-022-24 and 95-029-4. Blackline-resistant walnuts are approaching the level of commercial acceptability necessary for variety introduction. OBJECTIVES Blackline is serious virus disease of English walnuts when grafted onto rootstocks that are hypersensitive to the cherry leafroll virus (walnut strain). The UC Davis Walnut Improvement Program is developing selections that are resistant to blackline by incorporating hypersensitivity from Northern California black walnuts and then back-crossing to English walnuts. The objective of this project was to compare the nut characteristics of commercial interest of conventional walnut varieties versus blackline-resistant numbered selections from the UC Davis Walnut Improvement Program. SIGNIFICANT FINDINGS Some numbered blackline-resistant varieties from the UC Davis Walnut Improvement Program are approaching the level of commercial acceptability necessary for commercial introduction. Continued breeding of blackline-resistant varieties is essential to be able to release one or more of these varieties for commercial use in the near future. PROCEDURES One thousand gram samples of each selected walnut variety were collected at harvest, placed in mesh bags and dried at 110 degrees F in a laboratory drying oven. Samples were submitted to Diamond Foods, Inc, Stockton, CA for crackout analysis. Samples collected included the conventional varieties Payne, Serr (2), Howard (2), Tulare (3), Hartley (3), Chandler (3), Gillet, Sexton and 64-57 ( Bonturi ). Blackline-resistant varieties included 92-016-1 (2), 93-045-1 (2), 94-022-24, 94-026-20, 95-027-11, 95-027-23, 95-029-4, 96-017-12, and 96-027-8. California Walnut Board 53 Walnut Research Reports 2013
RESULTS The results of the crackout analysis for San Benito County samples in 2013 are shown in table 1. The characteristics summarized in the table are nut weights, percent large, sound nuts, percent mold, percent shrivel, percent edible yield, percent extra-light colored kernels, percent light colored kernels, percent light amber colored kernels, percent amber colored kernels, reflected light index (RLI) and relative value (RV). The 2013 season was characterized by many warm but few hot days in the Central Coast. Sunburn damage was not prominent in most orchards. Codling moth damage was light but walnut husk fly damage was mild to severe. Nuts damaged by walnut husk fly were not collected in samples utilized by this project due to their potential impact on nut quality. Each grower/location is shown in the column labeled LOC for location. The nut weights are mean nut weights per nut in grams and varied from 15.15 to 7.95 grams this season. The percent, sound nuts are the percentage of the nuts that are both in the large size category and where the shell is free from defects. The range this season was 100 down to 1 percent. The percent mold and percent shrivel are the percentage of the walnuts showing those defects on the kernel. There were few samples with either defect. The four color groups (extralight, light, light-amber and amber) are determined by comparison to a standard walnut color chart. There were very few light-amber or amber nuts this season. The RLI is a color determination for a whole sample made by bouncing light off the sample. Higher is lighter or better and the samples this year ranged from 59.30 to 51.60. RV is a way of determining the relative value of each sample based upon the formula used in previous years. A value of 1.00 (no units) is equivalent to a baseline variety with a 50.0% edible yield and a 55.0 RLI. A higher value is better and RV s ranged from 1.233 to 0.857 this year. There was very little mold in the 2013 season with most varieties at zero percent mold. One Hartley sample reached 7 percent mold. There was very little shrivel in the 2013 season. The variety 95-027-11 had the most at 9 percent. In table 2, the same crackout analyses are arrayed in order of high to low for each characteristic by variety name. Variation between growers and locations can be seen in some cases as more important than variety. For example, Tulare is near the top, the middle and the bottom of the reflected light index depending upon the grower and location. DISCUSSION The heaviest nuts (all above 13 g mean nut weight) were samples of Sexton, Gillet, 64-57, 94-026-20 and Payne. The lightest nuts (all less than 10 g mean nut weight) were samples of Chandler, 93-045-1 and 92-016-1. The highest percentage of large, sound nuts (99 or 100 percent) were samples of Chandler, 94-022-24, Payne, Tulare and Sexton. The lowest percentage of large, sound nuts (less than 50 percent) were samples of Chandler, 93-045-1 and 92-016-1. The highest percent edible yield (58% or higher) were samples of 95-029-4, Serr and 94-022-24.The lowest percent edible yield were three samples of Hartley at 40.3, 45.8 and 46.2 percent. Hartley might bring a higher price in-shell but most Central Coast Hartley walnuts are shelled. California Walnut Board 54 Walnut Research Reports 2013
One sample of Chandler walnuts had 100 percent extra-light kernels followed by samples of Tulare and Hartley at 95 percent. The variety 95-027-23 had no extra-light kernels. For RLI, the top varieties (59.00 or higher) were Howard, Chandler (2 samples) and Hartley (2 samples). The varieties with the lowest RLI (below 53.00) were 95-027-23 and one sample of Tulare. Finally for RV, the varieties with the highest value (all above 1.20) were Serr, 94-022-24 and 95-029-4. The lowest RV s (all less than 1.00) were the three Hartley samples and 95-027-11. Several of the numbered blackline-resistant varieties were competitive with conventional varieties in the common factors that result in high walnut value. This does not necessarily mean these varieties are ready for commercial introduction. For example, 94-026-20 is a vigorous tree that is slow to come into production and has had relatively light crops. However, it does indicate that the UC Davis Walnut Improvement Program is close to achieving a desirable blacklineresistant variety and some may already be suitable for locations with the highest incidence of the disease. ACKNOWLEDGEMENTS Thank you to Chuck Leslie and the Walnut Improvement Program at UC Davis for providing blackline-resistant grafting wood for propagating the trees in this project. Thank you to Diamond Foods, Inc., Stockton, CA for providing the crackout analysis of all walnut samples utilized in this project. California Walnut Board 55 Walnut Research Reports 2013
California Walnut Board 56 Walnut Research Reports 2013 TABLE 1: CRACKOUT COMPARISON OF BLACKLINE-RESISTANT AND CONVENTIONAL WALNUT VARIETIES -2013 % LARGE % EDIBLE %EXTRA- % LIGHT REFLECTED RELATIVE VARIETY ID # LOC NUT WT (g) SOUND % MOLD % SHRIVEL YIELD LIGHT %LIGHT AMBER AMBER LIGHT INDEX VALUE PAYNE 901 2 13.03 99 0 0 53.2 76 24 0 0 55.90 1.071 SERR 902 1 10.80 92 0 1 59.3 66 34 0 0 57.80 1.233 SERR 903 3 11.80 94 0 0 56.6 71 23 7 0 57.60 1.174 HOWARD 904 1 10.20 85 0 0 53.0 52 45 3 0 56.70 1.082 HOWARD 905 2 10.87 96 0 2 50.3 94 6 0 0 59.30 1.074 TULARE 906 1 10.56 89 0 0 57.5 28 68 5 0 51.60 1.069 TULARE 907 3 12.67 99 0 0 54.6 95 5 0 0 57.60 1.133 TULARE 908 4 13.00 95 0 0 53.1 84 16 0 0 59.00 1.129 HARTLEY 909 2 10.66 95 0 1 45.8 92 8 0 0 59.20 0.976 HARTLEY 910 3 12.51 97 0 0 46.2 73 24 3 0 58.90 0.979 HARTLEY 911 4 10.99 75 7 0 40.3 95 5 0 0 59.10 0.857 CHANDLER 912 1 8.85 44 0 0 51.8 76 22 1 0 58.40 1.089 CHANDLER 913 2 10.87 92 2 0 53.4 86 14 0 0 59.20 1.138 CHANDLER 914 4 12.66 100 0 0 49.6 100 0 0 0 59.30 1.059 GILLET 915 4 14.52 94 0 0 53.6 81 14 5 0 58.80 1.134 SEXTON 916 4 15.15 99 0 2 53.7 78 22 0 0 58.70 1.135 64-57 917 1 13.55 94 0 3 56.2 57 37 7 0 57.40 1.162 92-016-1 918 1 7.95 1 0 4 51.7 27 59 14 0 53.90 1.003 92-016-1 919 4 10.34 51 0 1 56.0 59 41 0 0 53.60 1.081 93-045-1 920 1 8.08 22 0 0 57.8 58 41 1 0 53.20 1.107 93-045-1 921 4 10.22 82 0 2 54.7 73 18 7 2 58.40 1.150 94-022-24 928 4 10.72 100 0 0 58.6 65 34 1 0 58.50 1.233 94-026-20 922 1 13.20 93 1 0 56.3 61 36 3 0 56.80 1.152 95-027-11 923 4 11.52 93 0 9 46.7 88 8 4 0 57.40 0.965 95-027-23 924 4 10.03 65 0 5 54.7 0 87 11 1 52.70 1.038 95-029-4 925 4 10.87 87 0 3 60.3 50 40 10 0 56.50 1.227 96-017-12 926 4 11.52 84 0 1 56.7 64 36 0 0 57.00 1.163 96-027-8 927 4 8.88 95 0 2 52.4 43 40 17 0 54.30 1.025
California Walnut Board 57 Walnut Research Reports 2013 TABLE 2: CRACKOUT COMPARISONS OF BLACKLINE-RESISTANT AND CONVENTIONAL WALNUT VARIETIES -2013 VARIETIES ARRAYED FROM HIGH TO LOW FOR EACH CHARACTERISTIC NUT WT (g) % LARGE SOUND % EDIBLE YIELD % EX-LIGHT REFLECTED LIGHT INDEX RELATIVE VALUE SEXTON CHANDLER 95-029-4 CHANDLER HOWARD SERR GILLET 94-022-24 SERR TULARE CHANDLER 94-022-24 64-57 PAYNE 94-022-24 HARTLEY HARTLEY 95-029-4 94-026-20 TULARE 93-045-1 HOWARD CHANDLER SERR PAYNE SEXTON TULARE HARTLEY HARTLEY 96-017-12 TULARE HARTLEY 96-017-12 95-027-11 TULARE 64-57 TULARE HOWARD SERR CHANDLER HARTLEY 94-026-20 HARTLEY TULARE 94-026-20 TULARE GILLET 93-045-1 SERR HARTLEY 64-57 GILLET SEXTON CHANDLER 95-027-11 96-027-8 92-016-1 SEXTON 94-022-24 SEXTON 96-017-12 SERR 93-045-1 PAYNE CHANDLER GILLET HARTLEY GILLET 95-027-23 CHANDLER 93-045-1 TULARE HOWARD 64-57 TULARE HARTLEY SERR TULARE CHANDLER 94-026-20 SEXTON 93-045-1 SERR 93-045-1 HARTLEY 95-027-11 GILLET SERR TULARE CHANDLER 95-029-4 SERR CHANDLER SERR 64-57 HOWARD SERR CHANDLER PAYNE 94-022-24 95-027-11 92-016-1 94-022-24 TULARE TULARE 96-017-12 96-017-12 HOWARD HARTLEY 95-029-4 HOWARD 94-026-20 94-026-20 PAYNE TULARE HOWARD 96-027-8 92-106-1 HOWARD TULARE 92-016-1 96-017-12 CHANDLER 93-045-1 95-029-4 CHANDLER 93-045-1 93-045-1 92-016-1 64-57 PAYNE 95-027-23 HOWARD HARTLEY HOWARD HOWARD 96-027-8 96-027-8 95-027-23 95-027-23 CHANDLER 95-029-4 92-016-1 92-016-1 96-027-8 92-016-1 95-027-11 96-027-8 92-016-1 HARTLEY CHANDLER CHANDLER HARTLEY TULARE 93-045-1 HARTLEY 93-045-1 93-045-1 HARTLEY 92-016-1 95-027-23 95-027-11 92-016-1 92-016-1 HARTLEY 95-027-23 TULARE HARTLEY