RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 75 



crispness of fruit grown where there is an abundance of soil moisture is 

 a matter of common knowledge. Bartlett pears grown with an extremely 

 limited water supply are distinctly and unpleasantly astringent, though 

 fruit of that variety under usual conditions is without astringency.^ 

 Peaches supplied early with abundant irrigation water but suffering 

 because of its lack late in the season, may be especially sweet and of 

 high quality but somewhat shriveled and of little commercial value.^^ 



Many claims are made for and against fruits grown in irrigated 

 sections. The discussion is based on the assumption that there is some 

 more or less direct influence of irrigation water on the composition and 

 consequently on flavor and quality. If this were the case the evidence 

 would not be conclusive, for fruit raised either in an irrigated or in an 

 unirrigated section is a product of the many factors constituting environ- 

 ment and not solely of differences in soil moisture. Chemical analyses 

 of many hundreds of fruits of different kinds grown with and without 

 the use of irrigation water, have led to the conclusion that in most decidu- 

 ous fruits differences between those irrigated and those not irrigated are 

 negligible.''^ Onl}^ in the strawberry were important differences found. 

 In that fruit the irrigated berries were lower in dry matter, sugar, acid 

 and crude protein and these differences were accompanied by a marked 

 difference in keeping quality. There appears to be little reason for the 

 popular belief that irrigated fruits as a rule are softer and more watery 

 than those not irrigated. It seems to make no difference whether the 

 soil receives its water from rains or through an irrigation flume. 



Disease Resistance and Susceptibility. — Correlated with the influence 

 of soil moisture on the texture and composition of the tissues of shoot, 

 leaf and fruit is its influence on resistance and susceptibility to certain 

 diseases. This has been noted many times in the common bacterial 

 fireblight of apples and pears. This disease works much more freely in 

 soft succulent tissues, slowing up or ceasing entirely as it reaches older 

 and harder wood. Thus high moisture content of the soil, forcing a more 

 succulent and vigorous growth, favors the development of the disease 

 and there are sections where the most practicable method of controlling 

 it on certain varieties is such culture as will maintain the soil moisture 

 at a point somewhat below the optimum for growth though well above 

 the wilting coefficient. An investigation of the relation between water 

 content of soil and the prevalence of fireblight in Idaho showed that 

 the soil moisture averaged 3 to 8 per cent, higher in badly blighted 

 orchards than in nearby orchards having little of the disease. ^^4 Similar 

 differences were found in the soil moisture content of slightly blighted 

 and badly blighted parts of the same orchard and in the soil under 

 diseased and disease-free trees. Extreme atmospheric humidity may 

 occasionally be a contributing factor. Presumably soil moisture exerts 

 equally great influence on susceptibihty or resistance to many other 



