Reproductive barriers in cassava: Factors and implications for genetic improvement

Cassava breeding is hampered by high flower abortion rates that prevent efficient recombination among promising clones. To better understand the factors causing flower abortion and propose strategies to overcome them, we 1) analyzed the reproductive barriers to intraspecific crossing, 2) evaluated pollen-pistil interactions to maximize hand pollination efficiency, and 3) identified the population structure of elite parental clones. From 2016 to 2018, the abortion and fertilization rates of 5,748 hand crossings involving 91 parents and 157 progenies were estimated. We used 16,300 single nucleotide polymorphism markers to study the parents’ population structure via discriminant analysis of principal components, and three clusters were identified. To test for male and female effects, we used a mixed model in which the environment (month and year) was fixed, while female and male (nested to female) were random effects. Regardless of the population structure, significant parental effects were identified for abortion and fertilization rates, suggesting the existence of reproductive barriers among certain cassava clones. Matching ability between cassava parents was significant for pollen grains that adhered to the stigma surface, germinated pollen grains, and the number of fertilized ovules. Non-additive genetic effects were important to the inheritance of these traits. Pollen viability and pollen-pistil interactions in cross- and self-pollination were also investigated to characterize pollen-stigma compatibility. Various events related to pollen tube growth dynamics indicated fertilization abnormalities. These abnormalities included the reticulated deposition of callose in the pollen tube, pollen tube growth cessation in a specific region of the stylet, and low pollen grain germination rate. Generally, pollen viability and stigma receptivity varied depending on the clone and flowering stage and were lost during flowering. This study provides novel insights into cassava reproduction that can assist in practical crossing and maximize the recombination of contrasting clones.

Flower abortion and yield of processing tomato according to irrigation depths

HIGHLIGHTS The number of flowers, the abortion rate, and the number of fruits per flower cluster directly influence processing tomato yield. Deficient or excessive irrigation levels impair flowering and increase the abortion of flowers of the processing tomato. Irrigation management is essential for the yield of processing tomato crops from the Brazilian Cerrado.

Grafting Improves Fruit Yield of Cucumber Plants Grown under Combined Heat and Soil Salinity Stresses

Improving the productivity of cucumber (Cucumis sativus L.) plants subjected to combined salinity and heat stresses is a significant challenge, particularly in arid and semi-arid regions. Gianco F1 cucumbers were grafted onto five cucurbit rootstocks and, together with an ungrafted control, were grown in Egypt in a net house with saline soil during the summer season over two years. The vegetative growth, yield, quality, biochemical, and mineral composition traits were measured. Although many differences were observed among treatments, in general, the grafted plants had a performance better than or similar to that of the ungrafted plants, based on the different parameters measured. In particular, the cucumber plants grafted onto the Cucurbita maxima × C. moschata interspecific hybrid rootstocks VSS-61 F1 and Ferro had the highest early and total marketable yields. These two rootstocks consistently conferred higher vigor to the scion, which had lower flower abortion rates and higher chlorophyll contents. The fruit quality and N, P, and K composition in the leaves suffered few relevant changes as compared with the control. However, the leaves of the VSS-61 F1 had higher catalase activity, as well as proline and Se contents, while those of Ferro had higher Si content. This study reveals that the grafting of cucumber plants onto suitable rootstocks may mitigate the adverse effects caused by the combination of saline soil and heat stresses. This represents a significant improvement for cucumber cultivation in saline soil under high-temperature stress conditions in arid regions.

EPIP-Evoked Modifications of Redox, Lipid, and Pectin Homeostasis in the Abscission Zone of Lupine Flowers

Yellow lupine is a great model for abscission-related research given that excessive flower abortion reduces its yield. It has been previously shown that the EPIP peptide, a fragment of LlIDL (INFLORESCENCE DEFICIENT IN ABSCISSION) amino-acid sequence, is a sufficient molecule to induce flower abortion, however, the question remains: What are the exact changes evoked by this peptide locally in abscission zone (AZ) cells? Therefore, we used EPIP peptide to monitor specific modifications accompanied by early steps of flower abscission directly in the AZ. EPIP stimulates the downstream elements of the pathway—HAESA and MITOGEN-ACTIVATED PROTEIN KINASE6 and induces cellular symptoms indicating AZ activation. The EPIP treatment disrupts redox homeostasis, involving the accumulation of H2O2 and upregulation of the enzymatic antioxidant system including superoxide dismutase, catalase, and ascorbate peroxidase. A weakening of the cell wall structure in response to EPIP is reflected by pectin demethylation, while a changing pattern of fatty acids and acyl lipids composition suggests a modification of lipid metabolism. Notably, the formation of a signaling molecule—phosphatidic acid is induced locally in EPIP-treated AZ. Collectively, all these changes indicate the switching of several metabolic and signaling pathways directly in the AZ in response to EPIP, which inevitably leads to flower abscission.

Organic foliar fertilizer to improve yield of cayenne pepper (Capsicum frutescens L.) grown off-season

Information on the most suitable and high-yielding cayenne pepper variety for an off-season growing in dryland is important. This research aimed to examine the effect of foliar fertilizer on growth and yield of off-season cayenne pepper in dry land. The experiment was conducted during the rainy season of 2020/2021 in a dryland with a sandy loam soil texture in the area of Gumantar, North Lombok, Indonesia. Four cayenne pepper varieties, namely Dewata 43 F1, Pelita F1, Taruna, and Sret, were treated with three concentration levels (0%, 0,5%, and 1,0%) of organic foliar fertilizer. The treatments were arranged in a factorial randomized block design with three replications. The results revealed that application of foliar fertilizer increased number of flowers and yield, and reduced flower abortion. Pelita F1 yielded the highest, 11.5% higher than Dewata 43 F1 and three-fold higher than that of the non-hybrid varieties when treated with 1.0% of fertilizer. Dewata F1 was harvested at 70 days after transplanting (dat), followed by 76, 105 and 105 dat for Pelita F1, Sret and Taruna, respectively. To maximize the use of the rainfall and prolong the harvest time, Pelita F1 and Taruna varieties are highly recommended for dryland areas.

Exogenous Gibberellic Acid and Cytokinin Effects on Budbreak, Flowering, and Yield of Blackberry Grown under Subtropical Climatic Conditions

In subtropical climates, inadequate winter chill limits blackberry (Rubus L. subgenus Rubus Watson) production by causing poor and erratic floral budbreak. To compensate for a lack of chilling, bud dormancy-breaking agents must be developed for subtropical blackberry production. Our previous study showed that gibberellic acid (GA3) promotes budbreak in three blackberry cultivars but has potential negative side effects on floral development in ‘Natchez’. 6-benzyladenine (6-BA) is a synthetic cytokinin that can act as an antagonist of gibberellins during floral transition. The objectives of this study were to evaluate cultivar × exogenous GA3 interactions, characterize dose effects of exogenous GA3, and examine synergistic effects of GA3 and 6-BA. Three field experiments were conducted in west central Florida. All spray treatments were applied at the end of the chilling period. In the first experiment, ‘Natchez’, ‘Navaho’, and ‘Ouachita’ were treated with GA3 at 0 or 99 g·ha−1. Budbreak was promoted by exogenous GA3 in all three cultivars (0.9% to 4.5% vs. 42.9% to 69.4%), but yield responses varied considerably. Exogenous GA3 increased the yield of ‘Navaho’ and ‘Ouachita’ by 560% to 931%, whereas it induced flower abortion and caused a 15% yield reduction in ‘Natchez’. In the second experiment, ‘Natchez’ was treated with GA3 at 0, 25, 99, or 198 g·ha−1. Budbreak increased linearly with GA3, but yield decreased exponentially with GA3 because of dose-dependent flower abortion. In the third experiment, ‘Natchez’ was subjected to five treatments: 1) water control; 2) GA3 spray application; 3) 6-BA spray application; 4) combined spray application of GA3 and 6-BA; and 5) sequential spray application of 6-BA at 9 days after GA3 application. Application rates were 99 and 47 g·ha−1 for GA3 and 6-BA, respectively. Exogenous 6-BA suppressed GA3-induced flower abortion only to a limited extent. As a result, GA3-containing treatments caused 65% to 83% yield reductions compared with the control (2382 vs. 410–823 g/plant). These results demonstrate that GA3 is a highly effective bud dormancy-breaking agent for blackberry. However, the drawback of GA3 is cultivar-dependent flower abortion, which cannot be fully mitigated by 6-BA. The use of GA3 can be an important management practice for subtropical blackberry production, but its practical implementation must consider cultivar-dependent responses.

Exploring Grapevine Phenology and High Temperatures Response Under Controlled Conditions

Climate change has challenged growers and researchers alike to better understand how warm temperatures may impact winegrape plant development across varieties. Yet multi-variety studies present challenges. Here we review studies of controlled warming on winegrape varieties alongside a new study of the budburst and flowering phenology of 50 varieties of Vitis vinifera subsp. vinifera in the lab, with a small set of plants exposed to higher temperatures (20, 26, 30, 34, and 37°C mean temperatures in growth chambers) during flowering. We found few studies have examined more than one variety, which may be due to the challenge of growing diverse varieties together. Indeed, we found high variability in flowering success across varieties in the lab (28 out of 50 varieties had no flowering), which made it impossible to study variety-specific response to temperature. Across varieties, however, we found results in line with a literature review (which we also present): higher temperatures did not have a significant effect on the rate at which vines progressed through the flowering stage, but higher temperatures did correlate with flower abortion. These results suggest a potential decrease in winegrape yields in a warmer climate due to flower abortion, but also highlight the challenges of understanding heat responses across many varieties.