from 'regions where the rainfall is very low during the period when seedlings are being 

 grown'. According to him, 'black rot' is little known in^rfie Puget Sound region in 

 Washington and in Pacific coast areas where summer precipitation is low. In these 

 regions, seed may be grown free from bacterial infection. 



Solanaceous Crops. Characteristic, and of great agricultural import, is the mode 

 of occurrence and distribution of some important diseases attacking potatoes and to- 

 matoes in Israel. These crops are afflicted in warm, humid climates by three high- 

 humidity- loving diseases, - P seudomonas solanacearum, Phytophthora infestans and 

 Cladosporium fulvum. In Israel they are to be found only in certain areas. P. solana- 

 cectnim was found here only on potatoes and even then, only in the one year, 1947, in 

 the coastal strip during a particularly damp spring and late autumn (Littauer, Volcani, 

 & Temkin, 1926). Phytophthora infestans is considered in our country to be a serious 

 menace to the winter- sown potatoes because of the abundant rain and the mild tem- 

 perature that prevails in that season. But the opposite is the case in the late spring 

 and the autumn, and the occurrence of the disease at this time is almost nil or very 

 scarce in the interior valleys, in upper Galilee and in the dry Negev. It is interesting 

 to note that until ten years ago, the disease was rather scarce even in the coastal re- 

 gion, but owing to the introduction of overhead sprinkling it has been on the increase. 

 It seems to be a known fact in Israel that morning sprinkling is less conducive to 

 disease than that carried out late in the day, as the latter method extends the time in 

 which there is high humidity, and with it the possibility of infection. Even in the 

 coastal belt, though, the disease is halted during the months of April and May by the 

 drying sirocco winds (khamsin), and it renews its development in June. 



Phytophthora infestans has been causing much damage to tomato crops within the 

 last years, and we are paying a great toll to this plant invader. It makes incursions 

 around the Sea of Galilee and in the coastal strip, but to a much lesser degree in the 

 interior valleys and the Negev. In the late spring it does not appear at all in the 

 Negev. 



Cladosporium fulvum is a lover of high humidity (Walker, 1950) and therefore is 

 limited to the spring and autumn in the coastal area and is not to be seen in the in- 

 terior valleys. 



Tomatoes are afflicted in our country and in many other Mediterranean countries 

 by the xerophilic plant disease Oidiopsis taurica, which attacks them heavily in the 

 interior valleys in the autumn, when the optimum relative humidity for the germination 

 of spores is less than 70% (Reichert, 1939b; 1949). Potatoes, in turn, are attacked 

 by an Oidium fungus which shows even greater xerophilic tendencies. Leaves are at- 

 tacked only in regions where humidity is lower than 50% (Reichert, 1949). 



Plantations 



Deciduous trees. Taphrina deformans is a serious malady of stone - fruit trees 

 in cooler countries. It appears in Israel chiefly on almond trees at higher altitudes in 

 early spring, since almond is an early bloomer. It occurs also to a lesser extent on 

 peaches. (Reichert, 1939c). 



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