PSOROSIS

separate troubles.

PSOROSIS

While many trees showed the early leaf syrriptoms of psorosis (1, 4), very few were found to exhibit the bark shelling and decline aspects of this virus disease.

TRISTEZA

Tristeza is an important consideration in a country where most trees are on sour orange root-stock. The sudden advent of tristeza virus in combination with an efficient vector like Toxoptera (Aphis) citricidus (Kirk.) could spell havoc, as it did in Argentina, where 20 years after introduction of this nefarious pair, five sixths of the 12 million trees of the country were killed.

A reservoir of tristeza already exists in Israel. Earlier reports (6, 9) showed that the virus was present in introduced varieties, but a later report (7) indicated that the tristeza virus also occurred in 82 out of 8,000 Shamouti orange trees in commercial groves.

A lookout was maintained for trees on sour orange stocks in a state of tristeza-like decline. Trees of lamoon belady (syn. Key lime) were also examined for the foliar vein-clearing symptoms indicative of tristeza. In no cases however were any suspicious symptoms seen.

While Toxoptera citricidus is not known at present in the Mediterranean area, two other species of aphid vectors were recorded from Palestine. One is the previously reported Aphis gossypii Glov., and the other. Toxoptera aurantii (Fonsc.), is reported here for the first time as occurring it Palestine. Neither species, however, is very effective in transmitting tristeza, and under conditions observed in the Gans. Strip, neither appears likely to do much damage. A more threatening prospect is the chance introduction of T. citricidus, either from India or from equatorial Africa.