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BY520-9 is being provisionally released as bulk seed for industry testing as a rootstock for peach and nectarine [Prunus persica (L.) Batsch] where root-knot nematode (Meloidogyne spp.), peach tree short life (PTSL) associated with ring nematode (Criconemella xenoplax (Raski) Luc & Raski], or both are a problem. BY520-9 consists of open-pollinated seed of 69 selections from B594520-9, which traces back to S-37 and Nemaguard.

Additional index words. Prunus persica, P. umbellata, Armillaria, peach tree short life, PTSL, root-knot nematode 'MP-29' rootstock has been jointly released for grower trial by the U.S. Department of Agriculture, Agricultural Research Service (Byron, GA) and the Florida Agricultural Experiment Station. 'MP-29' is suggested for trial as a rootstock for peach (Prunus persica L. Batsch) varieties on Armillaria root rot (ARR) [Armillaria tabescens (Scop.:Fr.) Dennis et al.] infested sites where peach seedling type rootstocks often fail to provide satisfactory tree longevity. Peach varieties budded onto 'MP-29' rootstock displayed significantly better resistance to ARR than did trees on 'Guardian' or 'Sharpe' rootstocks. Trees on 'MP-29' displayed resistance to peach tree short life (PTSL) comparable to that of trees budded onto 'Guardian' peach seedling rootstock. 'MP-29' also provides a marked reduction in tree vigor compared with peach seedling type rootstocks and may prove useful as a semidwarf rootstock where a less vigorous tree is preferred. Origin 'MP-29' is an interspecific hybrid developed by the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) at Byron, GA, from a cross made in 1994 between 'Edible Sloe', an apparent natural plum hybrid thought to include Prunus umbellata Elliot, and an advanced red-leafed peach rootstock selection from the Byron program, SL0014 (P. persica). 'MP-29' is reproductively sterile and is useful only as a rootstock. Description Unbudded trees of 'MP-29' display moderate vigor and a semispreading form. Leaves are red with a morphology intermediate be

Peach tree fungal gummosis caused by Botryosphaeria dothidea [(Moug.:Fr.) Cos & de Not.] is widespread throughout the southeastern United States. Until recently, its economic impact on peach [Prunus persica (L.) Batsch] has been impossible to estimate, since no effective controls were known. Significant, though not total, suppression of gummosis on `Summergold' peach trees was achieved with an intensive 5-year spray program with captafol. Captan was far less effective than captafol. Both trunk diameter and fruit yield were negatively correlated with disease severity. After eight growing seasons, trees treated with captafol were 18% larger than the untreated trees. Yield of mature captafol-treated trees was 40% to 60% high er than that of untreated ones. Following termination of the spray program after 5 years, disease severity gradually increased on both captafol- and captan-treated trees. However, through eight growing seasons, disease severity was significantly lower on captafol-treated trees. This study demonstrates that peach tree fungal gummosis significantly depresses tree growth and fruit yield on susceptible peach cultivars.

The effects of short-term soil flooding on gas exchange characteristics of containerized sour cherry trees (Prunus cerasus L. cv. Montmorency /P. mahaleb L.) were studied under laboratory conditions. Soil flooding reduced net CO2 assimilation (A) within 24 hours. Net CO2 assimilation and residual conductance to CO2(gr′) declined to ≈30% of control values after 5 days of flooding. Effects on stomatal conductance to CO2 (gS) and intercellular CO2 (Ci) were not significant during the 5 days of treatment. Apparent quantum yield (Φ) gradually declined to 52% that of controls during these 5 days. In a second experiment, CO2 response curves suggested that, initially, stomatal and nonstomatal limitations to A were of about equal importance; however, as flooding continued, nonstomatal limitations became dominant.