High-density mapping suggests cytoplasmic male sterility with two restorer genes in almond × peach progenies

Peach (Prunus persica) and almond (Prunus dulcis) are two sexually compatible species that produce fertile offspring. Almond, a highly polymorphic species, is a potential source of new genes for peach that has a strongly eroded gene pool. Here we describe the genetics of a male sterile phenotype that segregated in two almond ('Texas') × peach ('Earlygold') progenies: an F2 (T×E) and a backcross one (T1E) to the 'Earlygold' parent. High-density maps were developed using a 9k peach SNP chip and 135 simple-sequence repeats. Three highly syntenic and collinear maps were obtained: one for the F2 (T×E) and two for the backcross, T1E (for the hybrid) and E (for 'Earlygold'). A major reduction of recombination was observed in the interspecific maps (T×E and T1E) compared to the intraspecific parent (E). The E map also had extensive monomorphic genomic regions suggesting the presence of large DNA fragments identical by descent. Our data for the male sterility character were consistent with the existence of cytoplasmic male sterility, where individuals having the almond cytoplasm required the almond allele in at least one of two independent restorer genes, Rf1 and Rf2, to be fertile. The restorer genes were located in a 3.4 Mbp fragment of linkage group 2 (Rf1) and 1.4 Mbp of linkage group 6 (Rf2). Both fragments contained several genes coding for pentatricopeptide proteins, demonstrated to be responsible for restoring fertility in other species. The implications of these results for using almond as a source of novel variability in peach are discussed

Response of Prunus ferganensis, Prunus persica, and two interspecific hybrids to moderate drought stress

Prunus ferganensis (Kost. & Riab) Kov. & Kost, a close relative of the cultivated peach (Prunus persica (L.) Batsch.), is native to arid regions of central Asia and may possess traits valuable for improving drought tolerance of commercial peach varieties. One distinguishing feature of P. ferganensis is its prominent, elongated, unbranched leaf venation pattern, which behaves as a simple recessive trait in segregating populations of P. ferganensis x P. persica hybrids. To understand whether this trait could be used as a marker in breeding for drought tolerance, we investigated the association between leaf morphological and physiological parameters related to drought response in P. ferganensis, peach, and two interspecific hybrids, one which possessed the long-vein trait (BY94P7585), and another which did not (BY94P7589). The four genotypes were grafted onto ‘Guardian’ peach rootstock and grown in pots in a greenhouse for 3-4 months prior to drought treatments. Each genotype was divided into well-watered and water stressed groups, the latter accomplished by irrigating at 25-50% of rate of evapotranspiration (ET) measured in well watered plants (well watered plants received 100% of ET daily). Drought stress reduced photosynthesis (A) and leaf conductance (g) by 50-83%, reduced total leaf area per plant by 17-24%, but generally did not affect mid-morning leaf water potential, responses consistent with non-hydraulic signaling of decreased water availability by roots. Leaf gas exchange did not differ among genotype whether well-watered or stressed. Sorbitol accumulated in mature leaves in response to drought, but neither its amount nor its metabolism varied systematically with climatic adaptation among genotypes. Accumulation of transport sugars was highest in P. ferganensis, indicating that growth reduction may represent an important strategy for coping with drought in this species. P. ferganensis and both hybrids had higher ET than peach in the well-watered condition, and seemed to use water opportunistically – maintaining high rates of gas exchange and consequently ET when water was available, then avoiding low water potentials through stomatal closure as soil water declined. Leaf size (cm2 leaf-1) and specific leaf area (cm2 g-1 dry weight) were lower in the three genotypes with P. ferganensis background compared to peach, consistent with trends observed for other tree species collected along rainfall gradients. Although the long-vein trait per se does not provide a reliable marker for drought tolerance, the leaf size and leaf thickness traits of P. ferganensis may be incorporated into peach by use of this species in breeding programs

Simple-sequence repeat (SSR) markers of Japanese plum (Prunus salicina Lindl.) are highly polymorphic and transferable to peach and almond

Thirty-five polymorphic microsatellites were developed using a CT/AG enriched genomic library of Japanese plum cv. Santa Rosa. Twenty-seven of them detected a single locus and eight two or more loci. A high level of variability was observed in a set of eight cultivars for the 27 single-locus microsatellites: 5.7 average number of alleles per locus; 73% mean observed heterozygosity and 74% discrimination power. Most SSRs were transferable to peach (85%) and almond (78%).This research was funded in part by project RTA01-118-C2-2 from INIA (Spain).Peer reviewe