Kernel Fill Research Articles

Selection of Superior Properties of Walnut Genotypes in Ereğli-Halkapınar (Konya) and Ayrancı (Karaman) Walnut Population

This selection study was conducted to determine the walnut genotypes with superior characteristics grown from seeds in Ereğli and Halkapınar districts of Konya province and Ayrancı district of Karaman province between 2019-2022. In 2021 on the fruits taken, 8 genotypes in total, including 5 genotypes in shelled walnuts and 4 genotypes in kernels (1 genotype received high scores in both shelled and kernel walnuts) were found to be promising. In 8 genotypes selected, the shelled weight is 10.66-26.31 g, the kernel weight is 5.32-9.82 g, the kernel percentage is 37.33-57.91%, the shell thickness is between 1.06-1.90 mm, the shell color is “light” in 1 genotype, “moderate” in 4 genotypes, “dark” in 3 genotypes, kernel color is in 1 genotype “extra light”, “light” in 7 genotypes, remove of kernel from the shell was “easy” in all genotypes. Shell adhesion was “good” in all genotypes, cracking of the shell was detected “easy” in 7 genotypes, “moderate” in 1 genotype, shell texture was “smooth” in 3 genotypes, “moderate” in 4 genotypes, and “rough” in 1 genotype. Remove of kernel from the shell was determined “easy” in all genotypes. Kernel fill and healthy kernel percentage was determined as 100% in all genotypes. At the end of the research, 6 of the selected genotypes showed homogamy, 1 showed protogeny and 1 showed protandry flowering properties.

Description of Two Promising Walnut (Juglans regia L.) Selections with Lateral Bud Fruitfulness and Large Nuts

Walnut (Juglans regia) populations are considered a valuable genetic resource for genetic variability conservation and walnut cultivar improvement. In the current study, two walnut selections from Central Greece, “FM3” and “FM6”, were evaluated for their characteristics to determine their perspective as new cultivars. Their main phenological and pomological characteristics were assessed according to IPGR (1994) and UPOV-TG/125/6 (1999) criteria for 10 consecutive years and compared with “Chandler”. Results revealed that “FM3” presents high lateral flowering (70–80%), whereas “FM6” is 30–35%. Although the date of bud break and male blooming of both selections did not differ from “Chandler” (p > 0.05), the female blooming phase of “FM6” occurred earlier (p < 0.05) than “Chandler” and nut harvest was earlier than both “Chandler” and “FM3” (p < 0.05). Nut dimensions of both selections were higher than “Chandler” (p < 0.001). The mean in-shell nut weight and kernel weight of “FM3” were higher than “FM6” and “Chandler”, and those of “FM6” were higher than “Chandler” (p < 0.001). Other positive nut characteristics were their light kernel color, the well kernel fill, and the easy removal of the kernel halves. Thus, the current results indicate that “FM3” and “FM6” could be considered promising gene pools in crossbreeding activities.

Effect of Climatic Conditions Caused by Seasons on Maize Yield, Kernel Filling and Weight in Central China

In order to evaluate the effects of climatic conditions on maize grain yield (GY), kernel weight (KW), and kernel filling and identify the optimal climatic factors for GY and KW, 2-year field experiments in three seasons, i.e., spring (SPM), summer (SUM), and autumn (AUM), on maize were conducted in Central China. The results showed that SUM had more growing degree days (GDDs) than SPM and AUM due to the higher mean temperature (MT), and also resulted in higher temperature stress (killing degree days (KDDs)) in maize growth duration. Meanwhile, after silking, SPM and SUM had more GDDs and KDDs than AUM because of the higher MT, and the accumulated solar radiation (Ra) for SUM was significantly higher than for SPM and AUM. The GY of SPM was significantly higher than that of SUM and AUM, while SUM’s GY was always the lowest, because the GDDGD, MTGD, and KDDGD played significantly negative roles on GY. The final KW for SUM was always the lowest, with GDD, MT, KDD, and Ra causing significantly negative effects, and M△T and precipitation having significant positive effects, resulting in a lower kernel filling rate during the linear kernel filling period (KFRlkf) and a lower GDD at the maximum kernel filling rate (GDDKFRmax). Maize KFRlkf has significant negative linear dependences on GDD, MT, and Ra. In summary, because of the higher MT, KDD, and GDD during maize growth and kernel filling duration negatively affecting the maize kernel filling rate, the GY and KW for SPM were the highest, and for SUM, they were the lowest; therefore, farmers should plant SPM first and then AUM in Central China.

Impact of imposed root lodging on corn growth and yield

AbstractStrong winds combined with heavy rains can push corn (Zea mays L.) plants over and pull roots part way out of the soil. Weather events that bring these conditions are becoming more frequent in occurrence in the midwestern United States. Yield losses due to root lodging have been related to partial loss of root activity and reduced light interception, but also may stem from affected pollination and kernel fill. A field study was conducted in Ohio from 2018 to 2020 that simulated root lodging from strong winds imposed at V10, V13–14, VT–R1, or R3 growth stages in three modern hybrids. Plants were pushed perpendicular to row direction at the specified stage following natural rain or irrigation events. Differences in hybrids were recorded in this study, but each hybrid exhibited a similar response to lodging (hybrid × lodging interaction was not evident). Yield was reduced by 5, 22, 43, and 33% compared to non‐lodged control at V10, V13–14, VT–R1, and R3, respectively. Light interception in the upper canopy decreased when measured at R4 if lodged previously, and was of greater magnitude as lodging occurred later in the season. Poor pollination contributed to the large yield loss at VT–R1. In addition to reduced yield, increased vivipary and decreased kernel weights in the R3 treatments could further reduce grain quality. These yield losses from this study are greater than have been reported previously, and should be considered when assessing fields for severe wind damage in the future.

Kernel Water Relations and Kernel Filling Traits in Maize (Zea mays L.) Are Influenced by Water-Deficit Condition in a Tropical Environment.

Water deficit is a major limiting condition for adaptation of maize in tropical environments. The aims of the current observations were to evaluate the kernel water relations for determining kernel developmental progress, rate, and duration of kernel filling, stem reserve mobilization in maize. In addition, canopy temperature, cell membrane stability, and anatomical adaptation under prolonged periods of pre- and post-anthesis water deficit in different hybrids was quantified to support observations related to kernel filling dynamics. In this context, two field experiments in two consecutive years were conducted with five levels of water regimes: control (D1), and four water deficit treatments [V10 to V13 (D2); V13 to V17 (D3); V17 to blister stage (D4); blisters to physiological maturity (D5)], on three maize hybrids (Pioneer 30B80, NK 40, and Suwan 4452) in Expt. 1. Expt. 2 had four water regimes: control (D1), three water deficit treatments [V10 to anthesis (D2); anthesis to milk stage (D3); milk to physiological maturity (D4)], and two maize hybrids (NK 40 and Suwan 4452). Water deficit imposed at different stages significantly reduced maximum kernel water content (MKWC), kernel filling duration (KFD), final kernel weight (FKW), and kernel weight ear–1 while it increased kernel water loss rate (KWLR), kernel filling rate (KFR), and stem weight depletion (SWD) across maize hybrids in both experiments. The lowest MKWC under water deficit was at D3 in both experiments, indicating that lower KFR results in lowest FKW in maize. Findings indicate that the MKWC (R2 = 0.85 and 0.41) and KFR (R2 = 0.62 and 0.37) were positively related to FKW in Expt. 1 and 2, respectively. The KFD was reduced by 5, 7, 7, and 11 days under water deficit at D3, D4 in Expt. 2 and D4, D5 in Expt. 1 as compared to control, respectively. Water deficit at D5 in Expt. 1 and D4 in Expt. 2 increased KWLR, KFR, and SWD. In Expt. 2, lower canopy temperature and electrical conductivity indicated cell membrane stability across water regimes in NK 40. Hybrid NK 40 under water deficit had significantly higher cellular adaptation by increasing the number of xylem vessel while reducing vessel diameter in leaf mid-rib and attached leaf blade. These physiological adjustments improved efficient transport of water from root to the shoot, which in addition to higher kernel water content, MKWC, KFD, KFR, and stem reserve mobilization capacity, rendered NK 40 to be better adapted to water-deficit conditions under tropical environments.

A fine‐scale genetic linkage map reveals genomic regions associated with economic traits in walnut (Juglans regia)

AbstractA genetic linkage map of walnut containing 2,220 single nucleotide polymorphisms (SNPs) in 16 linkage groups (LGs) was constructed using an F1 mapping population from a cross between “Chandler” and “Idaho,” two contrasting heterozygous parents. Five quantitative yield traits, lateral fruitfulness, harvest date and three nut traits (shell thickness, nut weight and kernel fill) were then mapped on to linkage groups. A significant quantitative trait locus (QTL) in LG 11 with negative additive effects suggested heterozygote superiority in the expression of lateral bearing. A set of three QTLs explaining ~10% of the variation in harvest date was located in LG 1. Shell thickness, nut weight and kernel fill were under the control of two to three linked pleiotropic QTLs in LG 1 segregating from “Idaho.” The marginal positive additive effects of QTLs for harvest date, shell thickness and nut weight and small negative additive effects for kernel fill suggested that the QTLs had a marginal effect on the expression of these traits.

Genetic diversity of superior Persian walnut genotypes in Azadshahr, Iran.

Persian walnut (Juglans regia L.) is known to have originated in central and eastern Asia. Remnants of these wild populations can still be found in the Hyrcanian forest in north-eastern Iran. In this study, 102 individual walnut trees from four geographic populations in the Azadshahr province (Vamenan, Kashidar, Rudbar and Saidabad) were sampled. We characterized individual trees using 28 standard morphological traits. The range of traits varied widely for some economically important characteristics including nut weight (6.1-19.79g), kernel weight (2.9-9.4g), and kernel fill percentage (26.51-60.34%). After morphological evaluation, 39 superior individuals based on nut quality and kernel fill percentage were selected for further genetic analysis. Individual superior trees were genotyped using 10 simple sequence repeat markers (SSR) and genetic diversity. Number of alleles per locus ranged from 3 (WGA005) to 12 (WGA054). Clustering analysis of 10 SSR loci divided the genotypes into three main groups. PCoA analysis clearly sorted genotypes into one of four distinctive groups which aligned with the cluster analysis. All analyses showed that individuals from Saidabad were genetically distinct. Likewise, results indicated that the high level of genetic diversity in Azadshahr region walnuts may provide a diverse source for superior walnuts in walnut breeding programs.

Deletion Mutagenesis and Identification of Causative Mutations in Maize.

We describe a method for gamma-irradiation of mature maize seeds to generate mutants with opaque endosperm and reduced kernel fill phenotypes. We also describe methods for mapping mutants and identifying causal gene mutations. Using this method, a population of 1788M2 families and 47 Mo17×F2s showing stable, segregating, and viable kernel phenotypes was developed. For molecular characterization of the mutants, we utilized a novel functional genomics platform that combines separate Bulked Segregant RNA and exome sequencing data sets (BSREx-seq) to map causative mutations and identify candidate genes within mapping intervals. We also describe the use of exome capture sequencing of F2 mutant and normal pools to perform mapping and candidate gene identification without the need for separate RNA-seq (BSEx-seq). To exemplify the utility of the deletion mutants for functional genomics and provide proof-of-concept for the bioinformatics platform, we summarize the identification of the causative deletion in two mutants. Mutant 937, which was characterized by BSREx-seq, harbors a 6203-bp in-frame deletion covering six exons within the Opaque-1 gene on chromosome 4. Preliminary investigation of opaque mutant 1486 with BSEx-seq shows a tight mapping interval and associated deletion on chromosome 10.

Seven Days of Consecutive Shade during the Kernel Filling Stages Caused Irreparable Yield Reduction in Corn (Zea mays L.)

In monsoon climates, persistent shade is a troublesome weather condition with an impact on the growth and yield of corn (Zea mays L.). We imposed 7, 14, 21, and 28 days of consecutive shade (CS) on Gwangpyeongok and P3394 corn hybrids at the beginning of the kernel filling stages. Shade had little i...

A Population of Deletion Mutants and an Integrated Mapping and Exome-seq Pipeline for Gene Discovery in Maize.

To better understand maize endosperm filling and maturation, we used γ-irradiation of the B73 maize reference line to generate mutants with opaque endosperm and reduced kernel fill phenotypes, and created a population of 1788 lines including 39 Mo17 × F2s showing stable, segregating, and viable kernel phenotypes. For molecular characterization of the mutants, we developed a novel functional genomics platform that combined bulked segregant RNA and exome sequencing (BSREx-seq) to map causative mutations and identify candidate genes within mapping intervals. To exemplify the utility of the mutants and provide proof-of-concept for the bioinformatics platform, we present detailed characterization of line 937, an opaque mutant harboring a 6203 bp in-frame deletion covering six exons within the Opaque-1 gene. In addition, we describe mutant line 146 which contains a 4.8 kb intragene deletion within the Sugary-1 gene and line 916 in which an 8.6 kb deletion knocks out a Cyclin A2 gene. The publically available algorithm developed in this work improves the identification of causative deletions and its corresponding gaps within mapping peaks. This study demonstrates the utility of γ-irradiation for forward genetics in large nondense genomes such as maize since deletions often affect single genes. Furthermore, we show how this classical mutagenesis method becomes applicable for functional genomics when combined with state-of-the-art genomics tools.

Changes in Kernel Filling with Selection for Grain Yield in a Maize Population

Changes in Kernel Filling with Selection for Grain Yield in a Maize Population

Changes in Kernel Filling with Selection for Grain Yield in a Maize Population

ABSTRACTGenetic improvement in kernel filling characteristics has been an important contributor to hybrid maize (Zea mays L.) yield increases. However, changes in kernel filling characteristics have not been evaluated within the context of recurrent selection programs. The objective of this study was to determine if rate and duration of kernel filling and their interaction with plant density changed with long‐term recurrent selection for agronomic performance in the Iowa Stiff Stalk Synthetic (BSSS) population. Populations selected for improved grain yield and agronomic performance were compared with the unselected base population, BSSS, at average final plant densities of 4.7 and 6.6 seeds m−2 at two locations near Ames, IA in 2009 and 2010. Treatments were replicated three times per location in a split plot design. Selected populations had a longer period of kernel filling but did not have a higher rate of kernel filling. Selected populations also had reduced final kernel weight at higher plant density, whereas unselected populations did not differ in final kernel weight. Reduction in final kernel weight at high plant density in selected populations suggests that increases in grain yield at high plant density in selected populations resulted from components of grain yield other than final kernel weight.

Seasonal changes in nutrient content and concentrations in a mature deciduous tree species: Studies in almond (Prunus dulcis (Mill.) D. A. Webb)

Knowledge of the pattern of nutrient uptake and loss and the within-tree allocation of nutrients in trees is critical to the understanding of ecosystem nutrient fluxes and to the management of applied nutrients in agricultural ecosystems. Fluxes of nutrients in whole trees and determination of total annual uptake, nutrient allocation within organs and loss in annual organs were obtained in a mature commercial almond (Prunus dulcis) orchard managed with non-limiting irrigation under varied nitrogen (N) and potassium (K) fertilization regimes from 2008 through 2012. Whole tree nutrient dynamics were derived from multiple in-season measurements of nutrients in leaves and fruits and biomass in all years. Whole tree nutrient budgets in perennial tree parts were derived from whole tree excavations and tree coring in 2011 and 2012 when the orchard had reached >85% full canopy closure. The annual N increment in perennial tree organs was 21kg, 41kg, 44kg and 45kgha−1 for the four N application rates of 140kg, 224kg, 309kg and 392kgha−1 N, respectively. In this orchard maximum agronomic productivity (yield plus increment in tree size) was recorded with an N application rate of 309kgha−1. Under optimal N application the annual increment in P, K, Ca and Mg was 8kg, 38kg, 3.5kg and 2.8kgha−1. Total N in leaves in midsummer in 2012 (a low yield year) was 37kg, 43kg, 54kg and 58kgha−1 for the four N application rates. In contrast, total N in leaves at mid-summer in 2011 (high yield year) was 21kg, 28kg, 35kg and 39kgha−1 for the four N application rates. In years 2009 through 2011 nitrogen in fruit at harvest represented 90% of whole tree N fluxes. In trees provided just adequate N to achieve maximal yield (309kgha−1 in this experiment in years 2009–11), N, P, K, S, Ca and Mg export in fruit was 212kg–366kgha−1, 26kg–45kgha−1, 265kg–389kgha−1, 7.9kg–14.4kgha−1, 24.7kg–29.6kgha−1 and 15.9kg–22.6kgha−1, respectively. The majority of whole tree macro and micronutrient uptake occurred between anthesis and kernel fill with 35–50% of total N uptake occurring before 40 days after full bloom (DAFB) and 80–90% of the total N being accumulated by 112 DAFB coinciding with kernel filling. Over 70% of the total P and 65–80% of the total K was accumulated in fruits by mid-season. Ninety percent of total S, 80–90% of total Ca and 70–85% of total Mg accumulated in fruit by 112 DAFB. The findings from the study can be used for in-season fertilizer management according to plant demand based on expected yield.

THE PHENOLOGY OF EARLY FRUIT RIPENING IN PECAN

Twenty-two pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars were monitored weekly for stage of fruit development to establish how differences in fruit phenology ultimately define time of ripening. Simple techniques for season-long, field assessment of fruit expansion, kernel fill and shuck dehiscence were developed to allow for the uniform evaluation fruit phenology independent of cultivar differences in fruit size and weight. The earliest fruit ripening cultivars in this trial entered into the period of rapid fruit expansion over two weeks before cultivars that ripen late in the season. Once rapid fruit expansion began, the pace of fruit development for early-ripening cultivars was faster than later maturing pecans. Early ripening cultivars took the least amount of time to fully expand their fruits and achieve maximum ovule expansion (the water stage). Early maturing cultivars were also quicker to split shucks (ripen fruit) once kernel deposition was completed. The time required to deposit solid kernel tissue inside a fully expanded ovule was roughly the same for all early ripening cultivars (two weeks). Only extremely late maturing cultivars, or those cultivars generally not adapted to the 200 day growing season at this study’s location, took longer to fill their kernels (18-21 days). Charting the key phenological events that define time of fruit ripening for all 22 cultivars studied in this test illustrates that pecan fruit phenology is a continuously variable genetic trait. In addition, the simple methods assessing fruit phenology developed in this study may become an important tool for screening a large number new pecan clones for adaptation to northern pecan growing regions.

Leaf Photosynthesis in Nitrogen-starved ‘Western’ Pecan Is Lower on Fruiting Shoots than Non-fruiting Shoots during Kernel Fill

Photosynthetic function in nut trees is closely related to nitrogen (N) nutrition because much of tree N is held within the leaf photosynthetic apparatus, but growing fruit and seeds also represent strong N sinks. When soil N availability is low, nut trees remobilize and translocate N from leaves to help satisfy N demand of developing fruit. Our objective was to describe shoot-level impacts of pecan [Carya illinoinensis (Wangenh.) K. Koch.] fruiting on leaf N and photosynthesis (Pn) during kernel fill under a range of tree N statuses. Our study was conducted in a mature ‘Western’ pecan orchard near Las Cruces, NM. In 2009, 15 trees showing a range of N deficiency symptom severity were grouped according to leaf SPAD into low, medium, and high N status categories. Differential N fertilizer rates were applied to the soil around high and medium N trees to accentuate differences in N status among the three categories. Light-saturated leaf Pn was measured on fruiting and non-fruiting shoots during kernel fill in 2009 and 2010. After measurement of Pn, the leaflet and its leaflet pair partner were collected, dried, and analyzed for tissue N. Leaf N concentration was significantly lower on fruiting shoots than non-fruiting shoots on all three sampling dates. The tree N status main effect was also significant, whereas the two-way interaction of shoot fruiting status and tree N status was not. Photosynthesis of leaves on fruiting shoots was significantly lower than that of non-fruiting shoots on all sampling dates. These data suggest that N demand by the growing kernel reduced N in leaves on the same shoot. Consequently, Pn of those leaves was reduced. The effect of tree N status and shoot fruiting status was best summarized with an additive model where there is a larger relative reduction in leaf N and Pn for fruiting shoots on trees with low N status.

Effects of flower buds removal on seasonal starch storage and mobilization in fruiting and non-fruiting branches of pistachio trees cv. Mateur under dry and warm climate

Fruit trees need to store reserves to allow their survival during winter and for bud flush and leaf growth in the following spring. The current study investigated the effects of alternate bearing and flower buds removal on seasonal starch storage and mobilization in leaves, current shoot and one-year-old wood of fruiting and non-fruiting branches of ‘Mateur’ pistachio (Pistacia vera L.) trees in arid land. Four treatments were applied; T0: untreated trees, T1: removal of all flower buds for one year, T2: removal of all flower buds for two successive years and T3: removal of 50% of flower buds for each year. Annual starch storage and mobilization in fruiting and non-fruiting branches of pistachio trees appeared to be driven by crop load, nut development stage and carbohydrate demands. Starch concentrations in leaves, current shoot and one-year-old wood increased slightly in non-fruiting than in fruiting branches of pistachio. In ‘on’ trees (T0 and T3), one-year-old wood starch increased after the initial growth flush, but is mobilized during kernel fill and continued to decrease after nut harvest. Starch mobilization from current shoots of ‘on’ trees during the high demand period of stage III corresponded to the period of flower bud abscission. These results suggested that branch wood starch concentrations represent the overall balance between source and sinks. Subsequent flower buds removal (T1 and T2), leaves accumulated starch during the first and the third stage of nut growth, whereas, gradually increase of starch concentration occurred over the growing season for the current shoots and one-year-old wood. Starch deficiency in current shoots of ‘on’ trees could be responsible for bud drop and finally for alternate bearing. The yield patterns of pistachio trees cv. Mateur have not shown real evidence of alternate bearing in the experimental site. Flower buds removal (T1 and T2) allowed pistachio trees to achieve higher yield potential, while, these two treatments performed the lowest cumulated yield. Removal of 50% of flower buds (T3) did not cause a significant change in yield, compared to untreated trees, in each of the first three years, as well as in the total yield accumulation. When focusing on 2008, this treatment caused a significant increase in yield, compared to other treatments including the control. Current shoot starch status was also higher in 2008 in the 50% fruit removal treatment. If we isolate and focus on the results obtained in 2008, it appears that this treatment can cause more stable yields, possibly through an increase in current shoot starch content. Consequently, under severe climatic conditions of arid land, the annual pruning could be applied to equilibrate flower buds number and to improve the tree starch status.

Hormone Contents in Kernels at Different Positions on an Ear and Their Relationship with Endosperm Development and Kernel Filling in Maize

Kernels at the upper position of a maize ear usually show poorer filling and lower weight in contrast to those at the basal position.The mechanism has not been understood.The experiments were conducted using a maize cultivar Denghai 11,grown in both field and greenhouse conditions,to determine number of endosperm cells,kernel filling rate,and contents of zeatin(Z) + zeatin riboside(ZR),indole-3-acetic acid(IAA),abscisic acid(ABA),and gibberellin-3(GA3) in the kernels at different positions on an ear from silking to maturity.The results indicated that the maximum number of endosperm cells,maximum division rate of endosperm cells,mean endosperm cell division rate,maximum kernel filling rate,mean kernel filling rate and 100-kernel weight for kernels showed an order of basal position middle position upper position.During the active endosperm development and the active kernel filling period,contents of Z+ZR,IAA,and ABA in kernels were the greatest at the basal position,the mediate at the middle position,and the least at the upper position on an ear.The two experiments exhibited similar results.The endosperm cell division rate and kernel filling rate were very significantly and positively correlated with contents of Z+ZR,IAA,and ABA in kernels,whereas significantly and negatively correlated with content of GA3.The results suggested that a lower kernel weight at the upper position on a maize ear is mainly due to a smaller division rate of endosperm cells,leading to less number of endosperm cells,which is closely associated with lower contents of Z+ZR,IAA,and ABA,as well as higher content of GA3in the kernels during kernel filling.

Mature Pecan Orchard Floor Vegetation Management: Impacts on Tree Water Status, Nutrient Content, and Nut Production

Pecan [Carya illinoinensis (Wangenh.) K. Koch] growers are advised to control orchard floor vegetation when establishing new orchards, but there is not a set recommendation for vegetation control in mature orchards. The objective of this study was to measure the effect of orchard floor vegetation on water and nitrogen (N) status of flood-irrigated mature pecan trees. Four treatments studied were: completely vegetated orchard floor, vegetation-free inner area directly under the tree canopy with vegetation in the outer area, completely vegetation-free, and vegetated inner area under the canopy with a vegetation-free outer area. Treatments were organized as a 2 × 2 factorial structure with inner and outer treatment factors, both with levels vegetated and vegetation-free. Soil moisture and tree midday stem water potential (MSWP) were measured during irrigation cycles to evaluate the development of water stress in the pecan trees. Soil moisture data showed a significant outer main effect when the soil in the entire orchard was the driest, that is, just before irrigation events. Areas with vegetation cover that were exposed to full sun were significantly drier than shaded vegetated areas and vegetation-free areas in the orchard floor. However, this was not correlated with differences in tree water status as indicated by MSWP. Leaf tissue and soil analyses showed no significant differences in N concentrations among treatments in either year. Treatments with orchard floor vegetation in the outer area had significantly higher yield efficiency and marginally significant improvements in percent kernel fill and number of nuts per kilogram. Our findings suggest that there may be more benefits to maintaining orchard floor vegetation in mature orchards than were previously acknowledged.

Molecular Mapping of the Leaf Rust Resistance Gene Lr17a in Wheat

Wheat leaf rust, caused by Puccinia triticina Eriks., infects millions of acres of wheat (Triticum aestivum L.) and causes leaves to senesce prematurely, which in turn decreases yield by reducing the plant's ability to complete kernel fill. Lr17a, a leaf rust resistance gene in wheat, is present in many wheat varieties available today. The objective of this research was to identify molecular markers linked to Lr17a Microsatellite markers were used on a mapping population of 161 F2 lines made from a cross of Chinese Spring and Thatcher‐Lr17a Capillary fragment analysis was performed and eight markers were linked to Lr17a, of which Xgwm614 and Xwmc407 flanked Lr17a at genetic distances of 0.7 and 2.5 cM, respectively. An evaluation of cultivars with and without Lr17a, and grown in the midwestern United States, revealed that multiple alleles were present for all markers and little correspondence between alleles of closely linked markers and Lr17a was observed. Therefore, caution must taken when using them for marker‐assisted selection.

Seasonal carbohydrate storage and mobilization in bearing and non-bearing pistachio (Pistacia vera) trees

We analyzed annual carbohydrate storage and mobilization of bearing ("on") and non-bearing ("off") 'Kerman' pistachio (Pistacia vera L.) trees growing on three different rootstocks. On all rootstocks, carbohydrate storage in shoots and branches of "on" and "off" trees was lowest following the spring growth flush. In "off" trees, stored carbohydrates increased and remained high after the initial growth flush. In "on" trees, stem carbohydrates increased temporarily in early summer, but were mobilized in mid-season during kernel fill, and then increased again after nut harvest. During the dormant season, the only substantial differences in carbohydrate storage between previously "on" and "off" trees were found in the roots of the weakest rootstock. The annual carbohydrate storage and mobilization pattern in canopy branches of heavily cropped pistachio trees appeared to be driven by carbohydrate demands related to nut development and untempered by tree vigor. Mobilization of carbohydrates from current-season and 1- and 2-year-old stem wood of "on" trees during the primary period of kernel fill corresponded with the period of inflorescence bud abscission. Thus, the alternate bearing pattern associated with inflorescence bud abscission in 'Kerman' pistachio may be a function of mid-season mobilization of stored carbohydrates in current-season stems resulting in stimulation of inflorescence bud abscission.