Of 12 Duke avocado trees tested, 10 were found to be free of sun blotch virus infection. However, two trees without sun blotch symptoms were infected and apparently both are symptomless carriers. These transmit the virus through seeds to their seedling progeny and can cause infection of the scion tops that are worked on them when used as rootstocks. These studies demonstrate that it is necessary to test all Duke seed-source trees before using them as rootstock parents.