Agronomic response and water productivity of almond trees under contrasted deficit irrigation regimes

We investigated the long-term effects of different deficit irrigation (DI) options on tree growth, shoot and leaf attributes, yield determinants and water productivity of almond trees (Prunus dulcis, cv. Marta) grown in a semiarid climate in SE Spain. Three partial root-zone drying (PRD) irrigation treatments encompassing a wide range of water restriction (30%, 50% and 70% of full crop requirements, ET_c) and a regulated deficit irrigation treatment (RDI, at 50% ET_c during kernel-filling) were compared over three consecutive growth seasons (2004–2006) to full irrigation (FI). The results showed that all deficit irrigation treatments have a negative impact on trunk growth parameters. The magnitude of the reduction in trunk growth rate was strongly correlated through a linear relationship with the annual volume of water applied (WA) per tree. Similarly, a significant relationship was found between WA and the increase in crown volume. In contrast, leaf-related attributes and some yield-related parameters (e.g., kernel fraction) were not significantly affected by the irrigation treatments. Except in PRD₇₀, individual kernel weight was significantly reduced in the deficit irrigated treatments. Kernel yield, expressed in percent of the maximum yield observed in the FI treatment, showed a linear decrease with decreasing WA and a slope of 0.43, which implies that a 1% decrease in water application would lead to a reduction of 0.43% in yield. Water productivity increased drastically with the reduction of water application, reaching 123% in the case of PRD₃₀. Overall, our results demonstrate the prevalence of direct and strong links between the intensity of the water restriction under PRD – i.e., the total water supply during the growing season – and the main parameters related to tree growth, yield and water productivity. Noteworthy, the treatments that received similar annual water volumes under contrasted deficit irrigation strategies (i.e., PRD₇₀ and RDI) presented a similar tree performance.     

Plant based indicators for irrigation scheduling in young cherry trees

Using a correlation between trunk diameter fluctuation (TDF) and stem water potential (SWP) it appears possible to determine water deficit threshold values (WDTV) for young cherry trees. This correlation must be based on a significant effect between SWP and at least one variable associated with the vegetative or reproductive growth of the trees. The objectives of this study are: (1) to determine the effect of several irrigation treatments on vegetative and reproductive growth and the SWP of young cherry trees; (2) to determine the correlation between TDF and SWP, and; (3) to propose a first approximation of SWP and TDF water deficit threshold values for young cherry tree plants. The experiment was carried out between September and April of the 2005-2006 and 2006-2007 seasons, in Quillota, in the Valparaiso region, central Chile. The irrigation treatments consisted of applications of 50% (T₅₀), 100% (T₁₀₀) and 150% (T₁₅₀) of potential evapotranspiration (ET₀) over the two growing seasons, using a randomized complete block design (RCB). The effect of irrigation scheduling was observed on: apical shoot growth rate (GR_AS), branch cross-sectional area (BCSA), canopy volume (CV), annual length of accumulated growth (AL_AG) and productivity. This effect showed that the T₅₀ treatment caused lower SWP (measured pre-dawn), vegetative growth and productivity. The fruit quality variables (cracking and size) were not affected by the different treatments. Combining the vegetative growth, productivity and SWP results shows that the water deficit threshold value, as a first approximation, is between 50% and 100% of ET₀, and therefore the critical SWP for defining irrigation frequency should be close to −0.5 MPa. Upon applying a post-harvest drought period (14 days without irrigation), a linear correlation was determined both between SWP and maximum daily trunk shrinkage, MDS (R² = 0.69) and between SWP and trunk growth rate, TGR (R² = 0.57). Using these correlations and the SWP reference value, reference values were obtained for MDS (165 μm) and TGR (83 μm day⁻¹), which would permit automated control of water status in young cherry trees.     

Patterns and heritability of carboxylic acids and soluble sugars in fruits of apricot (Prunus armeniaca L.)

The investigation of acid and sugar content in an array of apricot cultivars and progenies indicates the existence of marked variability. Citric acid varied from 0.17 to 1.20% and malic acid from 0.21 to 1.51% on fresh weight. Fructose varied from 0.27 to 1.60%, glucose from 0.90 to 3.13% and sucrose from 1.92 to 6.92%. The estimate of heritability was high for total and main sugars, reaching over 0.50%. Acids generally showed low coefficients, although those for citric (0.27) and malic (0.36) were good. With the exception of one progeny, all genotype/year comparisons were not significant, showing constant patterns for acid and sugars over the years regardless of the variability in absolute values. This means that the patterns of each genotype are under genetic control. The wide range of diversity in acid and sugar content in apricot germplasm and the independent heritability for most of these compounds make it possible to breed and select cultivars with improved flavour on the basis of superior phenotypes.     

Discrimination between Japanese and Chinese Products using trace elements concentration of kernel in pickled Japanese apricot

pp. 875–880

The trace-element composition of kernel in pickled Japanese apricot (Prunus mume Sieb. et Zucc.) was determined using an inductively coupled plasma optical emission spectrometer in order to distinguish between Japanese products and Chinese products.

Strontium and barium concentrations in the kernels of Chinese products were 10 or more times those of the Japanese ones. When based on 8.0 mg kg^?1 of strontium concentration in kernel, 93.2% of sample was distinguished as Japanese products or Chinese ones.

Applying principal component analysis using 9 elements (Mn, Zn, Fe, Ni, Ba, Sr, Cu, Co, Cr), the pickled Japanese apricots tend to separate into two countries. Linear discriminant analysis (LDA) using 9 elements allowed a reasonable classification of pickled Japanese apricots according to the country of production.

The result of the analysis of K-nearest neighbors (KNN) was better than that of LDA.     

Morphological variation within collections of Moroccan almond clones and Mediterranean and North American cultivars

Summary Cultivated almonds (Prunus dulcis (Miller) D.A. Webb) in Morocco are still propagated from seeds by farmers to overcome transplant failure of grafted trees. Almond collections in southern Morocco conducted since 1975 have resulted in the selection of clones planted at 3 experimental stations. Principal component analysis (PCA) was used to compare kernel, nut, leaf, and growth habit characteristics among 67 selected Moroccan clones and 14 introduced cultivars. Clustering of clones from similar countries and collection areas would suggest the existence of different almond populations. The Moroccan clones did not cluster separately from the foreign cultivars. Three Moroccan clones had exceptionally large nuts and kernels while 7 selections had high yield potential due to high spur density. Moroccan selections tended to be characterized by small leaves in comparison to foreign cultivars. No evidence was found to suggest the existence of separate populations within the Moroccan almond germplasm.     

Stability of bacterial leaf spot resistance in peach regenerants under in vitro,greenhouse and field conditions

Summary Phenotypic stability of bacterial leaf spot resistance in peach (Prunus persica (L.) Batsch) regenerants, either selected at the cellular level for insensitivity to a toxic culture filtrate of Xanthomonas campestris pv. pruni or screened at the whole plant level for resistance to X. campestris pv. pruni, was investigated. A detached-leaf bioassay was used to evaluate the original regenerants again after three years in the greenhouse and also after a two to three year cycle of tissue culture propagation. Peach trees derived through micropropagation from the original regenerants were also evaluated after one to three years growth in the field. Although leaf spot resistance was retained in some regenerants over time in the greenhouse, following in vitro propagation, and under field conditions, resistance was either lost or not expressed in others. Regenerants # 19-1 and #156-6, derived from embryo callus of bacterial spot susceptible Sunhigh, were significantly more resistant than Sunhigh. High levels of resistance were exhibited in greenhouse plants and field-grown trees of regenerant #122-1, derived from embryo callus of moderately resistant Redhaven. This research provides additional evidence that selecting or screening for somaclonal variants with disease resistance is a feasible approach to obtaining peach trees with increased levels of bacterial spot resistance.Abbreviations TC Tissue-Cultured - TF Toxic culture Filtrate     

Inheritance of tree and fruit characters in progenies from crosses of sweet cherry (Prunus avium L.) cultivars

Summary Approximately 1000 seedlings from 20 combinations crossed in 1979, 1980 and 1981 (Theiler-Hedtrich 1985a) were tested for several characters: fruit set (yield), fruit size, fruit colour, formation of abscission layer and bleeding after fruit removal from fruit stalks, bacterial canker resistance, flowering and harvesting time. From progeny of crosses with Stella as pollinator, 56% (Vittoria × Stella) and 46% (Schüttler × Stella) of the seedlings were self-compatible, of which 14 were high yielding with good fruit size and quality. From the data recorded it can be concluded:fruit set is a recessive character; only 5 to 20% of very good yielding seedlings were obtained in different progeny, even if the parental plants were both very good croppers.Fruit juice and skin colour was in most progenies ‘black’ even if they were from combinations with ‘white’ varieties, e.g., Merton Glory or Schüttler. Only from the combination Schiittler (‘white’) × Stella (‘black’), 50% of the seedlings were ‘white’; Stella therefore is heterozygous for the character of fruit juice and skin colour.Fruit size is evenly distributed in progeny with respect to the fruit size of their parent plants.Abscission layer formation and non-bleeding is a genetically complex character. In combinations where both parent plants formed fruits with complete abscission layers and which were not bleeding after fruit removal from the stalk, this character was inherited only to 50% (Vittoria × Schüttler) or 85% (Vittoria × Frühe von der Weid) in the progeny. For the genetical control of this character further studies are necessary.Bacterial canker susceptibility was evenly distributed in seedlings from all combinations even if the highly resistant cv. Vittoria was used as one parent plant, thereby not confirming the expected results of a higher proportion of resistant seedlings from combinations with Vittoria.Flowering and harvest time of the seedlings from different combinations was within the range of the parent plants. Only in the combination of Vittoria × Stella (mid-to late-ripening season) one seedling out of 99 was found to form ripe fruits two weeks earlier than the parental plants. From the seedlings tested 40 have been chosen for further evaluation or genetical studies.     

Molecular genetic mapping of peach

Summary A project to develop a linkage map of the peach (Prunus persica) genome is underway using an F2 population segregating for several morphological characters and pest resistance e.g., nectarine (g), weeping shape (pl) and aphid resistance (Rml). The RAPID technique was used to analyse 270 plants. Linkage analysis of the F2 population was performed using the MAPMAKER software. Eight linkage groups were established and RAPID markers flanking thepl gene were found.     

Nutritional (Fe-Mn) interactions in ‘Big Top’ peach plants as influenced by the rootstock and by the soil CaCO3 concentration

Manganese (Mn) toxicity in plants is often not a clearly identifiable disorder and it can interfere with the absorption, translocation, and utilization of other elements such as Ca, Mg, Fe, and P. Soil conditions, management factors, and the use of different genotypes of rootstock can determine the degree of Mn toxicity and of interaction with other elements in the orchard. Five plants of the cultivar ‘Big Top’® grafted onto itself, onto plum rootstock ‘Mr.S.2/5’ and onto hybrid peach x almond rootstock ‘GF677’ were grown in 25-L containers under three treatments, 0, 20, 30% concentration of total lime, obtained by mixing powdered CaCO₃ to a sandy soil. Plants were fertilized with manure and a solid fertilizer early in April and irrigated in summer periodically with water rich in manganese. After just 28 d, active lime caused a decrease of chlorophyll SPAD index especially in plants grafted on itself, while those grafted on the tolerant ‘GF677’ rootstock behaved better than those grafted on ‘Mr.S.2/5.’ From June to September, irrigation caused increases in soil Mn concentration and Mn concentration in control plants. This caused first a serious defoliation in Big Top / Big Top plants and then a re-greening of cultivar grafted onto ‘Mr.S.2/5’ and ‘GF677,’ probably due to the interaction between iron and manganese at high pH. In particular the 20% CaCO₃ addition to the soil preserved the plants of cultivar grafted onto ‘Mr.S.2/5’ from Mn toxicity, as shown by their high chlorophyll content and growth and lower Mn leaf concentrations. Plants grafted onto ‘GF677’ rootstock showed the best behaviour under 30% CaCO₃ treatment associated to higher Fe(III)-reducing capacity and photosynthetic activity. Rootstocks and soil conditions (lime and waterlogging) influenced mineral status and growth of the peach cultivar ‘Big Top,’ particularly by interacting together and modifying Fe-Mn availability.     

Germination and net in vitro growth of peach, almond and peach-almond hybrid embryos in response to mannitol inclusion in the nutrient medium

Nine Prunus accessions were evaluated for germination and plantlet growth in an in vitro osmotic screening test using mannitol as an osmoticum. Embryos from diverse peaches, almonds and peach-almond hybrids were cultured in Woody Plant Medium, and in this same medium modified with the inclusion of 350 mM mannitol. Embryos were stratified in vitro for 60 days, induced to germinate for a two week period and then allowed to develop and grow for another 20 days prior to harvest. Fresh weights of both roots and shoots as well as percent germination were recorded at harvest. The main effects of nutrient medium, germplasm type (peach, peach-almond, almond) and specific Prunus accession were all highly significant (P = 0.01) with regard to fresh weight of roots and shoots. Embryo germination was affected significantly by the inclusion of mannitol in the nutrient medium and by the particular germplasm type (P=0.01 and P=0.05, respectively). Significant interactions of nutrient medium × Prunus accession and nutrient medium × germplasm type were also detected for both root and shoot fresh weights. Almond germplasm cultured in Woody Plant Medium with 350 mM mannitol produced significantly more roots and shoots than either peaches or peach-almond hybrids grown in the same medium. Peach-almond hybrid embryos were observed to germinate at a significantly higher frequency than peach embryos when averaged across both media. Results obtained in this study indicate a wide range of average plantlet fresh weight relative to the specific germplasm challenged in the osmotic screen. This revised version was published online in August 2006 with corrections to the Cover Date.