Establishing a Reference Baseline for Midday Stem Water Potential in Olive and Its Use for Plant-Based Irrigation Management

Midday stem water potential (SWP) is rapidly becoming adopted as a standard tool for plant-based irrigation management in many woody perennial crops. A reference or “baseline” SWP has been used in some crops (almond, prune, grape, and walnut) to account for the climatic influence of air vapor pressure deficit (VPD) on SWP under non-limiting soil moisture conditions. The baseline can be determined empirically for field trees maintained under such non-limiting conditions, but such conditions are difficult to achieve for an entire season. We present the results of an alternative survey-based approach, using a large set of SWP and VPD data collected over multiple years, from irrigation experiments in olive orchards located in multiple countries [Spain, United States (California), Italy, and Argentina]. The relation of SWP to midday VPD across the entire data set was consistent with an upper limit SWP which declined with VPD, with the upper limit being similar to that found in Prunus. A best fit linear regression estimate for this upper limit (baseline) was found by selecting the maximum R2 and minimum probability for various upper fractions of the SWP/VPD relation. In addition to being surprisingly similar to the Prunus baseline, the olive baseline was also similar (within 0.1 MPa) to a recently published mechanistic olive soil-plant-atmosphere-continuum (SPAC) model for “super high density” orchard systems. Despite similarities in the baseline, the overall physiological range of SWP exhibited by olive extends to about −8 MPa, compared to about −4 MPa for economically producing almond. This may indicate that, despite species differences in physiological responses to low water availability (drought), there may be convergent adaptations/acclimations across species to high levels of water availability. Similar to its use in other crops, the olive baseline will enable more accurate and reproducible plant-based irrigation management for both full and deficit irrigation practices, and we present tentative SWP guidelines for this purpose.

Efficiency of graft-transmitted JcFT for floral induction in woody perennial species of the Jatropha genus depends on transport distance

Flowering Locus T (FT) promotes flowering by integrating six genetic pathways. In Arabidopsis, the FT protein is transported from leaves to shoot apices and induces flowering. However, contradictory conclusions about floral induction via graft-transmitted FT in trees were reported in previous studies. We obtained extremely early-flowering transgenic woody Jatropha curcas by overexpression of J. curcas FT using Arabidopsis thaliana SUC2 promoter (SUC2:JcFT) and non-flowering transgenic J. curcas by RNA interference (RNAi), which were used to investigate the function of graft-transmitted JcFT in floral induction in woody perennials. Scions from five wild-type species of the Jatropha genus and from JcFT-RNAi transgenic J. curcas were grafted onto SUC2:JcFT rootstocks. Most grafted plants produced flowers in 1–2 months, and the flowering percentage and frequency of various grafted plants decreased with increasing scion length. Consistently, FT protein abundance in scions also decreased with increasing distance from graft junctions to the buds. These findings suggest that FT proteins can be transmitted by grafting and can induce the floral transition in woody perennials, and the efficiency of graft-transmitted JcFT for floral induction depends on the scion length, which may help explain previous seemingly contradictory observations regarding floral induction via graft-transmitted FT in trees.

Fruit Set in Avocado: Pollen Limitation, Pollen Load Size, and Selective Fruit Abortion

Avocado is a woody perennial fruit crop originating in Central America and Mexico domesticated and cultivated in the Americas since pre-Columbian times, currently cultivated in subtropical, tropical, and Mediterranean climates worldwide, with increasing importance in international trade. Avocado shows an exuberant flower production that, however, results in a very low fruit set reflected in a massive abscission of flowers and fruitlets. Several factors are involved in this behavior, and, in this work, we have focused on pollination limitation. The results obtained show that pollen deposition takes place at the female and male stages during the avocado flowering season and that the percentage of flowers with pollen on the stigma varies along the flowering season, probably due to changes in temperature that affect not only the floral behavior but also pollinator activity. However, no embryo or endosperm development took place when pollination occurred during the male flowering phase. Thus, the low number of pollen grains landing on the stigmas of female stage flowers observed under natural pollination conditions might not be enough to ensure a good yield. The production of an excess of flowers and subsequent flower drop of most of the flowers provides the opportunity of a selective fruitlet drop depending on the genotype of the embryo since fruits derived from outcrossing showed higher chances of reaching maturity. Moreover, an important competition for resources occurs among developing fruits and new vegetative growth, conferring importance to the time of flower fertilization for effective fruit set.

Morphological, Physiological, and Molecular Responses of Sweetly Fragrant Luculia gratissima During the Floral Transition Stage Induced by Short-Day Photoperiod

Photoperiod-regulated floral transition is vital to the flowering plant. Luculia gratissima “Xiangfei” is a flowering ornamental plant with high development potential economically and is a short-day woody perennial. However, the genetic regulation of short-day-induced floral transition in L. gratissima is unclear. To systematically research the responses of L. gratissima during this process, dynamic changes in morphology, physiology, and transcript levels were observed and identified in different developmental stages of long-day- and short-day-treated L. gratissima plants. We found that floral transition in L. gratissima occurred 10 d after short-day induction, but flower bud differentiation did not occur at any stage under long-day conditions. A total of 1,226 differentially expressed genes were identified, of which 146 genes were associated with flowering pathways of sugar, phytohormones, photoperiod, ambient temperature, and aging signals, as well as floral integrator and meristem identity genes. The trehalose-6-phosphate signal positively modulated floral transition by interacting with SQUAMOSA PROMOTER-BINDING-LIKE PROTEIN 4 (SPL4) in the aging pathway. Endogenous gibberellin, abscisic acid, cytokinin, and jasmonic acid promoted floral transition, whereas strigolactone inhibited it. In the photoperiod pathway, FD, CONSTANS-LIKE 12, and nuclear factors Y positively controlled floral transition, whereas PSEUDO-RESPONSE REGULATOR 7, FLAVIN-BINDING KELCH REPEAT F-BOX PROTEIN 1, and LUX negatively regulated it. SPL4 and pEARLI1 positively affected floral transition. Suppressor of Overexpression of Constans 1 and AGAMOUSLIKE24 integrated multiple flowering signals to modulate the expression of FRUITFULL/AGL8, AP1, LEAFY, SEPALLATAs, SHORT VEGETATIVE PHASE, and TERMINAL FLOWER 1, thereby regulating floral transition. Finally, we propose a regulatory network model for short-day-induced floral transition in L. gratissima. This study improves our understanding of flowering time regulation in L. gratissima and provides knowledge for its production and commercialization.

Effects of Drip Irrigation Design on a Lemon and a Young Persimmon Orchard in Semi-Arid Conditions

Drip irrigation is presently widely recognized as the most efficient irrigation system that can be used in woody perennial crops. However, uncertainties exist on the more appropriate agronomic design to employ. Here, we summarized the research carried out for three seasons in two young woody perennial crops (persimmon and lemon) in southeastern Spain. Several irrigation designs were compared by maintaining a similar amount of water application but varying the number of emitters and pipelines in each row in the orchard. In the lemon trial, the agronomic irrigation design was additionally combined with different irrigation regimes, comparing full irrigation (FI) with sustained deficit irrigation (SDI). In the persimmon trees, which were still at the juvenility stage, varying the number of emitters per tree or the number of drip lines per tree row, neither affects tree performance nor fruit yield in two out of the three seasons. However, over the entire experimental period, the relative trunk growth increased when more emitters were employed. In the lemon trial, carried out with trees that had reached commercial production, the FI, compared with SDI, increased trunk growth and average fruit weight, while a reduced number of fruits per tree without affecting total yield was observed in the third year of experimentation. The number of emitters per tree only had an effect the first year, increasing lemon fruit weight when the number of drippers per tree increased. In addition, fruit composition was not consistently affected by the irrigation design. It is concluded that, for a given irrigation dose, irrigation frequency, and soil conditions (loam-clay texture), in both very young and more mature trees, increasing the number of emitters or the wetted area only had some slight positive effects on tree performance.

Contrasting a reference cranberry genome to a crop wild relative provides insights into adaptation, domestication, and breeding

Cranberry (Vaccinium macrocarpon) is a member of the Heath family (Ericaceae) and is a temperate low-growing woody perennial native to North America that is both economically important and has significant health benefits. While some native varieties are still grown today, breeding programs over the past 50 years have made significant contributions to improving disease resistance, fruit quality and yield. An initial genome sequence of an inbred line of the wild selection Ben Lear, which is parent to multiple breeding programs, provided insight into the gene repertoire as well as a platform for molecular breeding. Recent breeding efforts have focused on leveraging the circumboreal V. oxycoccos, which forms interspecific hybrids with V. macrocarpon, offering to bring in novel fruit chemistry and other desirable traits. Here we present an updated, chromosome-resolved V. macrocarpon reference genome, and compare it to a high-quality draft genome of V. oxycoccos. Leveraging the chromosome resolved cranberry reference genome, we confirmed that the Ericaceae has undergone two whole genome duplications that are shared with blueberry and rhododendron. Leveraging resequencing data for Ben Lear inbred lines, as well as several wild and elite selections, we identified common regions that are targets of improvement. These same syntenic regions in V. oxycoccos, were identified and represent environmental response and plant architecture genes. These data provide insight into early genomic selection in the domestication of a native North American berry crop.

Analysis of genetic diversity among different Rose (Rosa) genotypes using morphological and molecular markers (ISSR)

Rose is a woody perennial of the genus Rosa within the family Rosaceae. In this study, phylogenetic relationship among seven different genotypes of Rose (Rosa) was determined using ISSR primers and morphological parameters. DNA was isolated using CTAB method with 0.5% of CTAB concentration. Out of 50 ISSR primers, 16 primers gave reproducible banding pattern with all the seven genotypes of Rose while others failed to produce polymorphism. A total of 108 bands were obtained with an average polymorphism of 54.69% and an average of 9.06 bands per primer. The average similarity was found to be 0.69 among all the seven genotypes using Jaccard’s similarity coefficient. On basis of polymorphism cluster analysis divided them into two major groups separating one genotype (light pink) from rest of the six genotypes and principle coordinate analysis confirmed the results. A parallel correlation was found between the morphological parameter (flower diameter) and the results of ISSR analysis as both of them divided the seven genotypes into two main groups.