ISHS Acta Horticulturae 193: XIII International Symposium on Fruit Tree Virus Diseases
ROLE OF INFECTED POLLEN IN HORIZONTAL TRANSMISSION OF CHERRY LEAF ROLL VIRUS, THE CAUSAL AGENT OF WALNUT BLACKLINE DISEASE |
| Authors: | S.M. Mircetich, A. Rowhani |
| Abstract:
Blackline (BL) disease of English walnut trees (Juglans regia) propagated on J.hindsii or Paradox and several other Juglans spp. other than J.regia is caused by a strain of the cherry leaf roll virus (CLRV-W). The virus spreads naturally in California's commercial walnut orchards. We consistently recovered CLRV-W in pollen and nuts from BL-affected English walnut orchard trees with ELISA and bioassays. CLRV-W was also detected in 3–5 % of 890 English walnut seedlings grown from nuts of 6 different naturally BL affected trees. To determine a possible role of pollen in natural spread of CLRV-W in orchards, immature pistillate flowers on CLRV-W free English walnut trees (cvs Vina, Eureka, Lompoc, Hartley, Franquette and Ashley) were covered with pollen-proof bags. Pistillate flowers at the most receptive stage were hand pollinated with CLRV-W infected or CLRV-W free English walnut pollen. One hundred fifty to 200 nuts and 150 to 300 spurs from each of two trees that received CLRV-W infected pollen were tested for CLRV-W. ELISA indicated that CLRV-W from infected pollen was transmitted into 3.7 to 18.5 % of the nuts and 1.9 ro 14.2 % of the spurs depending on the walnut cultivar. No CLRV-W was detected in any of the 50 nuts or 100 spurs from comparable trees of the same 6 walnut cultivars pollinated with CLRV-W free pollen. Apparently CLRV-W is transmitted by pollen into pistillate flowers and subsequently systemically infects nuts, spurs and mother English walnut trees. | |
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