The relationship between nutrients in extracted xylem sap and the susceptibility of fruit trees to silver‐leaf disease caused by Stereum purpureum (Pers.) Fr.

Abstract

S U M M A R YXylem sap was extracted from cut branches of stone-fruit and pip-fruit trees at different times of the year, and analysed for nitrogen and carbohydrate content. Growth of Stereumpurpureum was measured in the different sap samples in vitro. Nitrogen and carbohydrate levels in xylem sap from peach trees were highest in late winter and early spring, and these samples supported most growth of S. purpureum. At full bloom the levels of nitrogen and carbohydrate in xylem sap from stone-fruits (peach, nectarine, plum, cherry) were several times greater than in sap from pip-fruits (apple, pear), and the growth of S. purpureum in sap from stone-fruits was approximately ten times that in sap from pip-fruits.The results suggest that seasonal variations in susceptibility of stone-fruits to silver-leaf disease, and the greater susceptibility of stone-fruits than of pip-fruits, are due to differential ability of their xylem saps to support growth of S. purpureum.

Protection of fruit-tree pruning wounds against silver-leaf disease by immediate spray applications of captafol

“…purpureum was increasing (Dye 1967;Beever 1970). Thirty trees were pruned using modified secateurs described in the Appendix and each cut was sprayed immediately with 0.8% captafol (I % Difolatan 80 wp in water) until completely wet.…”

“…Fr. Pruning is frequently carried out in July and August when weather conditions are often highly favourable for spore release by C. purpureum (Dye 1974) and for the establishment of infections (Brooks & Moore 1926;Dye 1967;Beever 1970). Prompt application of antimicrobial paints, e.g., 'Prunteci', on the pruning cuts is an effective method of wound protection (Dye 1971).…”

Factors affecting Chondrostereum purpureum infection of Salix

“…Little has been published concerning the infection process of C. purpureum., except that it occurs mainly within xylem tissues, particularly within the lumen of xylem vessels and that nutrients are obtained from xylem sap (BINTNER 1919;BEEVER 1970). Also, basidiospores are thought to be sucked a considerable distance into vessels by the transpiration stream (BROOKS and MOORE 1926).…”

“…BROOKS and MOORE (1926) showed that fresh wounds on pear trees were highly susceptible to infection whereas it was very difficult to infect month old wounds and impossible to infect three month old wounds. Also there are reports (BROOKS and MOORE 1926;DYE 1967;BEEVER 1970) that the susceptibility of various host genera to C. purpureum varies throughout the year.…”

“…For instance, DYE (1967DYE ( , 1972 reported that peach and nectarine trees pruned in summer or autumn were less likely to become infected than if pruned in winter or early spring and GADGIL and BAWDEN (1982) reported that more wounds of E. delegatensis were infected when pruned during spring and summer than in autumn and winter. BEEVER (1969 and reported that levels of nitrogen and carbohydrate in xylem sap extracted from stone fruits (peach, nectarine, plum, cherry) in full bloom were several times greater than in sap from pip fruits (apple, pear) and that growth of C. purpureum in the former was ten times more. BEEVER (1970) suggested that this differential ability of xylem sap to support growth explained the seasonal variation in the susceptibihty of stone fruits.…”