Leaf development,net assimilation and leaf nitrogen concentrations of five Prunus rootstocks in response to root temperature

Rootstocks differentially influence tree physiology and these differences may be due to varying responses to root zone temperature (RZT). To determine if this is the case, the physiology, leaf development and nitrogen relationships of five different Prunus rootstocks with chill requirements between 100 and 1100 h were examined during and after growth at RZTs of 5, 12 and 19 °C for 6 weeks. RZT correlated positively with leaf numbers, expansion rates and final leaf area, and significant differences existed among the rootstocks in the magnitude of these parameters at different RZTs. In particular, leaf expansion and area were less affected at low RZT in the low chill varieties. Net assimilation (A_n), leaf nitrogen (N%) and photosynthetic nitrogen use efficiency (A_n/N) also correlated positively with RZT: again, there were differences in the magnitude of these parameters among the rootstocks. No associations amongst A_n, N% or A_n/N could be found for the rootstocks; hence, they all differed in their physiological responses to RZT. Low RZT alone was sufficient to reduce A_n and decreased both leaf area and photosynthetic activity. Leaf expansion was related to N%, as the varieties with the lowest N% also had the lowest expansion rates. Infrared thermography of the cv. Golden Queen showed a negative correlation between RZT and leaf temperature with leaves of plants at the lowest RZT being 2 °C warmer than ambient whilst those at the highest RZT were 2 °C cooler than ambient. These differences were due to transpiration, as transpiration for the variety used decreased with reducing RZT. Transpiration from the other rootstock varieties was lowest at the 5 °C RZT but, depending on variety, at 12 °C was either higher, lower or the same as that from plants whose roots were at 19 °C. Together, the results of this study explain some of the rootstock-induced changes in tree growth and suggest the need to incorporate seasonal changes in RZT into development models for peaches.     

Cross-transferable polymorphic SSR loci in Prunus species

This work reports the transferability and polymorphism of previously reported SSRs in 10 Prunus species. The availability of a large number of SSRs in the genus Prunus makes marker choice random, while preventing comparison of results in fingerprinting studies. The availability of SSR markers, polymorphic in a wide sample of Prunus species, would facilitate marker choice, while allowing the comparison of results. In this work, microsatellite markers useful for analyzing 10 different Prunus species (P. persica, P. dulcis, P. armeniaca, P. domestica, P. insititia, P. salicina, P. cerasifera, P. avium, P. cersus and P. mahaleb) were searched through screening SSRs previously reported to be conserved and/or polymorphic in more than one Prunus species. A selected group of 13 SSRs, transferable to the 10 species, was analyzed in terms of their usefulness for analyzing these species. The amplification range, polymorphism and variability detected by these loci are reported. The information provided will be useful for Prunus genetic studies as well as conservation and management of Prunus germplasm resources.     

Genetic characterization of different demes in Prunus persica revealed by RAPD markers

DNAs of 180 accessions in 10 demes in Prunus persica were amplified with twenty-two, 10-base primers selected from 200 arbitrary primers using Randomly Amplified Polymorphic DNA (RAPD) technology. One hundred and eighty loci were observed and recorded. With statistical analyses of the data from the study, genetic diversity of the demes was expressed as follow: yellow peach group > honey peach group > flat peach group > red leaf peach group > crisp peach group > bitao group and juicy peach group > nectarine group > shouxingtao group > weeping peach group. Genetic variations among and within groups by AMOVA analyses were 11.9, 88.1%, respectively. Demes clustered by UPGMA modified from NEIGHBOR procedure of PHYLIP Version 3.5, the edible peaches of which were combined as a section, while the ornamental species were classified into separate sections. Through analyses of genetic diversity and genetic structure, the results could provide molecular biological evidence for conservation and utilization of P. persica germplasm.     

Piriformospora indica promotes adventitious root formation in cuttings

Adventitious root formation in excised plant shoots is a crucial process in the vegetative propagation of many plant species, and insufficient rooting causes substantial losses in the propagation industry. Based on the various physiological effects on whole plants described for the basidiomycete Piriformospora indica, it was hypothesized that inoculation of the substrate with this endophyte should promote the generation and growth of adventitious roots in cuttings. Inoculation experiments were conducted to study the effects of P. indica on adventitious rooting in three plant species. Inoculation with P. indica dramatically enhanced the number and length of the adventitious roots in pelargonium and poinsettia. Root colonization parameters suggest that the interaction between the endophyte and cuttings had already occurred before physical contact. In contrast, petunia showed no rooting response to P. indica inoculation. Very fast root formation in this plant indicates that a minimum time period for the fungus–plant interaction is required for establishment of a promoting effect. P. indica-based biotechnology is proposed as a new tool for improving plant propagation systems of plant species or cultivars with low to moderate capacity of adventitious root formation.     

Evaluation of the effectiveness of soil-applied plant derivatives of Meliaceae species on nitrogen availability to peach trees

We assessed the effect of soil-applied derivatives of melia (Melia azedarach L.) and neem (Azadirachta indica A. Juss) on nitrogen (N) soil availability, root uptake and peach (Prunus persica L.) growth. First we evaluated the effectiveness of experimentally prepared amendments made with fresh ground melia leaves or commercial neem cake incorporated into the soil as nitrification inhibitors, then we evaluated the effect of fresh ground melia fruits and neem cake on growth and N root uptake of potted peach trees, and on soil microbial respiration. Soil-applied fresh ground melia leaves at 10 and 20 g kg⁻¹ of soil as well as commercial neem cake (10 g kg⁻¹) were ineffective in decreasing the level of mineral N after soil application of urea-N as a source of mineral N, rather they increased soil concentration of nitric N and ammonium N. The incorporation into the soil of fresh ground melia fruits (at 20 and 40 g kg⁻¹) and neem cake (at 10 and 20 g kg⁻¹) increased N concentration in leaves of GF677 peach × almond (Prunus amygdalus) hybrid rootstock alone or grafted with one-year-old variety Rome Star peach trees. An increase in microbial respiration, leaf green color and plant biomass compared to the control trees were also observed. The Meliaceae derivatives did not affect, in the short term (7 days), N root uptake efficiency, as demonstrated by the use of stable isotope ¹⁵N, rather they promoted in the long term an increase of soil N availability, N leaf concentration and plant growth.     

Root system traits of Mahonia aquifolium and its potential use in soil reinforcement in mountain horticultural practices

The structural changes of Hungarian agriculture in 1989 led to many mountain horticultural farms being abandoned. These structural changes have modified land use patterns which often resulted in decreasing slope stability in mountainous farms. Mahonia aquifolium has been cultivated in Hungary for over half a century for ornamental purposes; however its possible application in shallow slope stabilization has not been discussed. This paper presents the first results on the root morphology, and root tensile strength of M. aquifolium and determines its efficiency for soil protection in horticultural farming practice. Measurements were carried out on M. aquifolium seedlings from cultivated (C) and non-cultivated (NC) soil conditions. The C and NC specimens were measured and compared for root area ratio (RAR) and root tensile strength (T_R). These results were then compared with other species for which data was available. Results showed that M. aquifolium plants from C soil conditions had a significantly higher mean RAR with depth than M. aquifolium plants from NC soil conditions. The mean T_R results showed no significant difference between M. aquifolium plants from C and NC environments. The study also showed that M. aquifolium's root structure is comparable as soil protection with the other species although a higher degree of soil reinforcement by roots was obtained with C M. aquifolium specimens. M. aquifolium roots could represent effective soil protection. Moreover the plant is well suited to the demands of small-scale horticultural farm practices under mountainous conditions.     

The S-RNase-based gametophytic self-incompatibility system in Prunus exhibits distinct genetic and molecular features

Most Prunus fruit tree species exhibit a homomorphic gametophytic self-incompatibility (GSI) system, in which specificity of self/nonself-recognition is controlled by products encoded within the S locus. In the pollination event, a self-incompatibility (SI) reaction is triggered when the same “S allele” specificity is expressed in both the pollen and pistil. During the last two decades, much progress has been made in our understanding of the molecular basis of the gametophytic self-incompatibility system in Prunus. Identification of the pistil S and pollen S determinants led to the development of PCR-based S genotyping and marker-assisted selection for self-compatible (SC) individuals. Molecular and genetic analyses of Prunus SC S haplotypes and polyploid sour cherry (Prunus cerasus) reveal the possible existence of a distinct SI/SC recognition mechanism in the S-RNase-based GSI system of Prunus. This review summarizes the current molecular knowledge of the S-RNase-based GSI system in Prunus with reference to data collected for S-RNase-based GSI in other plants and its potential usefulness in SC breeding.     

Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato

Tomato spotted wilt (TSW) disease is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic film mulches affect both the incidence of TSW, and plant growth and yield of tomato. The objective of the present study was to determine the effect of root zone temperature (RZT) as affected by plastic film mulch on the manifestation of symptoms of TSW, and growth and yield of tomato plants either artificially inoculated with tomato spotted wilt virus (TSWV) or under natural TSW infection. In artificially inoculated plants as well as in plants under natural TSW infection, vegetative top fresh weight (FW) and fruit FW both increased with the length of time after transplanting that the plants remained free from TSW symptoms. The root zone temperature was highest under black mulch (seasonal mean = 27.5 °C), followed by gray (27.0 °C), silver (25.8 °C), and white (24.8 °C) mulches. The plants grown on black mulch showed the earliest appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields compared to plants on the other mulches. In conclusion, utilization of plastic mulches that created conditions of high RZT stress resulted in reduced plant growth and yield and predisposed the plants to earlier expression of TSW symptoms compared to plants grown at RZTs more favorable to tomato plant growth (optimal RZT = 26.1 °C [Díaz-Pérez, J.C., Batal, K.D., Granberry, D., Bertrand, D., Giddings, D., Pappu, H., 2003. Vegetative top growth and yield of tomato grown on plastic film mulches as affected by the appearance of symptoms of Tomato spotted wilt virus. HortScience 38, 395–399]). Since these plant responses to TSW under heat stress occurred in artificially inoculated plants as well as in plants under natural TSW infection, high RZTs probably affected the plants directly, independently of any possible effects on the thrips vectors.     

Rootstock influences the response of pistachio (Pistacia vera L. cv. Kerman) to water stress and rehydration

Pistachio cultivation requires the use of rootstock because grafting is the only form of vegetative propagation. The main commercial rootstocks are Pistacia integerrima L., Pistacia atlantica Desf., Pistacia terebinthus L. and Pistacia vera L. Pistachio is considered to be a drought and saline-resistant crop; however, there is little information describing varietal responses of rootstocks to water stress. Some studies have suggested that P. terebinthus L. is the most drought and cold resistant rootstock. The effect of the rootstock on the water relations of the grafted plant is crucial for improving crop performance under water stress conditions and for developing the best irrigation strategy. This work studied the physiological response to water stress of pistachio plants (P. vera L. cv. Kerman) grafted onto three different rootstocks P. terebinthus L., P. atlantica Desf. and a hybrid from crossbreeding P. atlantica Desf. × P. vera L. Plant physiological responses were evaluated during a cycle of drought and subsequent recovery in potted plants. Parameters measured were soil moisture, trunk diameter, leaf area, leaf number, leaf and stem dry weight, stem water potential, leaf stomatal conductance. The results showed different responses of cv. Kerman depending on the rootstock onto which it had been grafted. The hybrid rootstock was associated with a higher degree of stomatal control and reduced leaf senescence compared to P. atlantica and P. terebinthus, despite being associated with the most vigorous shoot growth. P. terebinthus enabled very effective stomatal control but was also associated with the most rapid leaf senescence. P. atlantica was associated with less vigorous shoot growth and similar levels of water stress as occurred with the others rootstocks under conditions of high evaporative demand, which was associated with lower stomatal control. The selection of the most effective rootstock choice for different environmental conditions is discussed.     

Evaluating foliar nitrogen compounds as indicators of nitrogen status in Prunus persica trees

Mobile nitrogen (N) forms may be better N indicators of the N status of trees than total nitrogen (TN) due to their higher sensitivity to increasing N supply. A field experiment was carried out over a 3-year period to compare foliar concentrations of total N (TN), soluble N (SN), chlorophyll (Minolta SPAD readings), NH₄–N and NO₃–N as indicators of soil N availability in nectarine, Prunus persica L. Batsch, cv. ‘Fantasia’ (grafted on ‘Nemaguard’ peach, P. persica × P. davidiana) trees. Young trees were exposed to a range of fertilizer-N application rates. Based on correlation analysis, the best association between leaf N compounds with soil N supply and trunk diameter and/or fruit yield was obtained with TN and chlorophyll SPAD readings. Leaf concentrations of mobile N compounds (NH₄–N and NO₃–N) increased more than any other N compound under high N supply; however, their inconsistency among years and low leaf concentration difficult their use as N indicators. The optimum foliar TN for growth decreased with tree age, 4.4%, 3.6% and 3.3% in non-bearing 1-year-old trees, non-bearing 2-year-old trees and 3.3 fruit-bearing 3-year-old trees. The optimum SPAD readings were 40 in 2-year-old trees and 42 in 3-year-old trees. Stable N compounds (TN and chlorophyll SPAD) could be used to N diagnosis in the zone of N deficiency, and soluble N compounds (NH₄–N and NO₃–N) to diagnoses N excess.     

Screening Capsicum species of different origins for high temperature tolerance by in vitro pollen germination and pollen tube length

Successful fruit set depends on several reproductive processes including pollen germination and tube growth processes. An experiment was conducted to determine the effects of temperature on pollen germination characteristics and to identify species/genotypic differences in Capsicum using the cumulative temperature response index (CTRI) concept. Pollen was collected from plants of seven genotypes from five Capsicum species, adapted to various parts of the world and grown outdoors in large pots. The pollen was subjected to in vitro temperatures ranging from 15 to 50 °C at 5 °C intervals. Pollen germination and tube lengths were recorded for all species after 24 h of incubation at the respective treatments. Species/genotypes differed significantly for in vitro pollen germination percentage and pollen tube length with mean values of 78% and 734 μm, respectively. The mean cardinal temperatures (T_min, T_opt, and T_max) averaged over genotypes, were 15.2, 30.7, and 41.8 °C for pollen germination and 12.2, 31.2, and 40.4 °C for pollen tube growth. The CTRI of each species/genotype calculated as the sum of eight relative individual stress response values, such as maximum pollen germination, maximum pollen tube length; T_min, T_opt, and T_max temperatures of pollen germination, and pollen tube lengths, identified species tolerance to high temperatures. Capsicum annum cv. Mex Serrano from Mexico was identified as tolerant, C. chacoense cv. 1312 and C. spp. cv. Cobanero from Argentina and Guatemala, respectively as intermediate and C. frutescens cv. Early Spring Giant from China, C. annum cv. Long Green from South Korea, C. spp. cv. NM89C130 and C. pubescens cv. 90002 from Guatemala as sensitive to high temperatures. The tolerant species/genotypes can be used in breeding programs to develop new genotypes that can withstand high temperature conditions both in the present climate and particularly in a future warmer climate.     

S-RNase based S-genotyping of Japanese plum (Prunus salicina Lindl.) and its implication on the assortment of cultivar-couples in the orchard

Determination of the genetic compatibility between self-incompatible cultivars is crucial in agriculture. The Rosaceae family carries the S-RNase-mediated gametophytic self-incompatibility (GSI) system. Each haplotype is conferred by an S-locus. The S-locus contains two highly polymorphic genes, S-RNase and SFB, which are characteristic of each haplotype and therefore these genes are ideal markers for molecular S-genotyping. In this study 43 Japanese plum cultivars grown in Israel were S-genotyped based on their S-RNase gene sequences. Four alleles, S^b, S^c, S^e and S^h are widespread and together are responsible for 87% of the S-haplotypes therefore many of the cultivar combinations are semi-compatible. In Israel semi-compatibility was shown to correlate with low yield. However, two cultivars, ‘Wickson’ S^fS^k and ‘Shiro’ S^fS^g carry rare S-haplotypes and, therefore, are fully compatible with most of the analyzed cultivars.     

Comparative analysis of genetic diversity in Prunus L. as revealed by RAPD and SSR markers

RAPD and SSR markers were used for genetic diversity evaluations among 15 genotypes selected from the genus Prunus L. Altogether 40 RAPD primers and 21 primer pairs designated for microsatellite loci were applied on the whole group of genotypes.     

Light quality affects in vitro adventitious rooting and ex vitro performance of cherry rootstock Colt

The effect of light quality on in vitro rooting of cherry rootstock “Colt” was studied to evaluate adventitious root development, ex vitro acclimatization and plant growth performance. Adventitious rooting was dependent on the light quality to which the microcutting were exposed. Highest number of roots per microcuttings was recorded under dichromatic light (blue + red). This response could be ascribed to the control of a strong synergistic interaction between phytochromes and blue light photoreceptors. Red light was more effective on root elongation than blue light. In this response a strong synergistic interaction between phytochromes and blue light photoreceptors was suggested. The effect of light quality on the number of root/explant affected the plant during acclimation, scoring the highest level of plant survival in the blue-, red- and blue + red-exposed plantlets. The light quality effect was also observed under greenhouse culture conditions, as shown by growth parameters at the end of six months in plants growth. No specific role was observed for the photoequilibrium of phytochrome. The results reported in this work show that plantlets exposed to different light quality, during the in vitro rooting phase, retain the light quality effects in the subsequent plant acclimatization and greenhouse plant growth phase.     

Phenotypic variability and genetic structure in plum (Prunus domestica L.), cherry plum (P. cerasifera Ehrh.) and sloe (P. spinosa L.)

In the present study, phenotypic variability of 80 plum (Prunus domestica L.) varieties maintained in the French National Plum Collection was evaluated with 19 quantitative traits. In addition, genetic diversity and genetic structure was studied in three plum species (P. domestica L., Prunus cerasifera Ehrh. and Prunus spinosa L.) using chloroplast DNA (cpDNA) markers and five single sequence repeat (SSR) loci. Based on phenotypic traits, some varieties, such as mirabelle plums, grouped together. Bayesian structure analysis was used to identify different genetic groups, whereby damson plums were clearly distinguished from greengage plums. When examining the three species together, a higher level of cpDNA allelic richness was found in P. cerasifera and in P. spinosa than in P. domestica where only five cpDNA haplotypes were detected in the national plum collection, with one main haplotype that accounted for 80% of the varieties studied. P. domestica cpDNA haplotypes tended to group together with P. cerasifera haplotypes whereas most of P. spinosa haplotypes formed a separate cluster. SSR markers were somewhat able to distinguish the three species. These results provide some clues as to the origin of plum and the various plum varieties. Our results also provide useful information for the management of plum genetic resources.     

Evaluation of apricot resistance to Plum pox virus (Sharka) in controlled greenhouse and natural field conditions

In this study we compare the evaluation of Plum pox virus (Sharka) resistance of 29 apricot genotypes in controlled greenhouse conditions by grafting onto infected ‘GF305’ peach seedlings growing in pots, and in natural conditions by grafting onto infected 5-year-old apricot trees growing in the orchard. Apricot genotypes evaluated were initially classified into three groups: susceptible to PPV (presence of PPV symptoms and ELISA positive in greenhouse and field assays), resistant (absence of PPV symptoms and ELISA negative in both assays) and undetermined (evaluated differently in both assays). Results showed a similar behavior against Plum pox virus in both assays in 20 out of the 29 apricot genotypes studied (69%). However, in the other nine genotypes results were different (31%). Evaluation in field was more accurate, detecting a higher number of susceptible genotypes, probably due to the higher inoculation pressure in the old trees in comparison with the GF305 rootstocks in pots. However, greenhouse evaluation let to work in controlled isolated conditions with a higher number of genotypes. This situation is greatly required in areas where Sharka is not widely spread. Greenhouse evaluation could be then the first screening method to evaluate Plum pox virus resistance of apricot genotypes, and could be complemented with the evaluation onto infected trees in natural conditions in insect-proof quarantine shelter.     

Early detection of graft incompatibility in apricot (Prunus armeniaca L.) using phenol analyses

The study investigated the role of phenols in apricot graft incompatibility. Assays of phloem with cambium from 1-year-old apricot trees of cultivars Marlen, Leskora and Betinka which were grafted on the rootstocks of different genetic origin: M-LE-1, Lesiberian, MY-KL-A, Tetra, Penta, Green Gage, Julior, MRS 2/5 and Isthara were analysed with HPLC (together 23 scion/stock combinations). The phloroglucinol, catechin, p-coumaric acid and further non-identified phenols with the retention time 23–25 and 30 min were determined. The content of individual phenol compounds was related to specific cultivar/rootstock combination. The minimum number of statistical significant differences in the phenol content between tissues above and below graft union was established in homospecific combinations (P. armeniaca/P. armeniaca). Cultivars Marlen, Leskora and Betinka differ in the degree of compatibility or incompatibility with rootstocks. The pattern of non-identified phenol 23 in different graft combinations is similar to catechin and p-coumaric acid.     

Evaluating variability of root size system and its constitutive traits in hot pepper (Capsicum annum L.) under water stress

The importance of root size system has long been recognized as crucial to cope with drought conditions. This investigation was conducted to: (i) evaluate the variability in root size system of hot pepper at maturity; (ii) estimate the effect of root size system on yield under drought conditions; and (iii) effect of water stress on xylem vessel development and total xylem cross-sectional area in roots of hot pepper cultivars. Twelve diverse hot pepper cultivars were grown in wooden boxes with two different water treatments, normal and in 50% water application as water deficit condition. Mean primary root length (PRL) showed a significant positive correlation with final fruit yield at normal as well as stressed condition. Total dry mass of fruit was reduced by 34.7% in drought treatments (DI) compared to full watered treatment (FI). At harvest, water-stressed plants had 21% lower root dry weight mass but higher root:shoot ratio other than FI. PRL, lateral root density, total xylem area per root cross-section showed a significant positive relationship with fruit yield. Also, lateral root density was higher in cultivars with higher xylem density, particularly in tolerant cultivars. Lateral root density (r = 0.847, P < 0.001) and total xylem cross-sectional area in root (r = 0.926, P < 0.001) were tightly related with total biomass production. The importance of root traits contributing to withstand drought in hot pepper is discussed.     

Comparison of the use of morphological,protein and DNA markers in the genetic characterization of Iranian wild Prunus species

In this study, the genetic diversity of four Iranian wild Prunus species including Prunus eleagnifolia, Prunus hauskenchtii, Prunus scoparia and Prunus lycioides were investigated using morphological, protein and DNA markers. DNA markers included nuclear and chloroplast SSRs and self-incompatibility (S) allele amplification. At the morphological level, leaf width showed significant differences between the four wild Prunus species. Concerning fruit and kernel characters, their values are relatively similar indicating the high degree of homoplasy described in Prunus. Nuclear SSR markers have been the most abundant markers with a higher polymorphism in comparison with morphological, protein and chloroplast SSR markers. Results also indicated the high variability present in the S locus. On the other hand, the correlation between the clustering based on DNA markers and protein were in general low. Dendogram performed using nuclear and chloroplast SSR indicated a more diffuse clustering between the wild almond species probably due to the natural introgression of genes observed in these wild almond species. Data from the analysis of the total protein seems to be more accurate to establish taxonomy relationships in these very close wild species.