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Detection of Xylella fastidiosa Wells et al. by enzyme-linked immunosorbent assay indicated that plums (Prunus hybrids) had higher absorbance values than peaches [Prunus persica (L.) Batsch]. The slip-budded trees had lower readings than those that were chip budded; however, the scion × method interaction was significant. Further comparison of slip vs. chip budding indicated that the lower absorbance value of slip budding occurred in plums only; there was no difference between budding methods in peach.

Differences in heat requirements for blooming and leafing were investigated in peach [Prunus persica (L.) Batsch] using artificially chilled excised shoots and potted trees. `Della Nona' and `BR-1' have high heat requirements; `Planalto', `Sunlite', and `Eldorado' are intermediate; and `Precocinho' and `Riograndense' have low heat requirements. Prolonged chilling enhanced leafing more than blooming. Flower and vegetative buds have different heat requirements during ecodormancy.

Two trials involving 20 Prunus rootstocks were conducted under greenhouse conditions to screen for resistance to root-knot nematode [Meloidogyne javanica (Treub.) Chitwood]. Many of the tested materials are interspecific hybrid rootstocks and represent new commercial peach (P. persica Batsch) and plum (Prunus sp.) releases or experimental genotypes of Spanish, French, and Italian origin. In the first trial, the rootstocks Adesoto 101 (P. insititia L.), Bruce (P. salicina Lindl. × P. angustifolia Marsh.), Ishtara, AC-952 (P. insititia), Garnem [P. dulcis (Mill.) D.A. Webb × P. persica], Cadaman [P. persica × P. davidiana (Carr.) Franch], and Orotava (P. salicina) were immune or resistant to a mixture of 10 isolates of M. javanica. The remaining rootstocks, Myrocal (P. cerasifera Ehr.), Montclar (P. persica), and Adafuel (P. dulcis × P. persica), were susceptible. In the second screening trial, the plum rootstocks Adesoto 101, Adara (P. cerasifera), Myro-10 (P. cerasifera), Constantí (P. domestica L.), and AD 105 (P. insititia) were immune to the root-knot nematode. Cadaman, G × N No. 17 (P. dulcis × P. persica), and Tetra (P. domestica) were resistant. Laroda F1OP (P. salicina), Myro-almond (P. cerasifera × P. dulcis), and the peach–almond hybrids Mayor, Adafuel, and Sirio were susceptible.

Total cellular DNA has been extracted from leaves and\or seed of Prunus dulcis, P. persica, P. mira, P. davidiana, P. persica subsp. ferganensis, and P. triloba. Chloroplast restriction fragments have been visualized by Southern blot analysis using heterologous probes from a petunia chloroplast library. Analysis of preliminary data separates the species into three groups. The first contains P. dulcis, P. mira, and P. davidiana; the second P. kansuensis, P. persica, and P. persica subsp. ferganensis; and the third P. triloba.

PCR amplification using oligos for cytosolic glyceraldehyde-3-phosphate dehydrogenase yields genomic fragments approximately 1kb in size from P. dulcis and P. triloba. Sequence analysis will be performed to determine species relationships at the gene level.