ROLE OF INFECTED POLLEN IN HORIZONTAL TRANSMISSION OF CHERRY LEAF ROLL VIRUS, THE CAUSAL AGENT OF WALNUT BLACKLINE DISEASE

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.

XIII International Symposium on Fruit Tree Virus Diseases

S.M. Mircetich, A. Rowhani

https://doi.org/10.17660/ActaHortic.1986.193.20