Ethephon-Induced Abscission of Oil Palm Fruits at Optimal Bunch Ripeness and Retting Period to Improve Commercial Seed Production

Oil palm seed producers typically require 10 months of various processes from pollination to seed germination to produce commercial dura × pisifera hybrid seeds. Conventional forced fruit shedding from underripe fresh fruit bunches (FFB) usually causes seed damage and an extended retting period (incubation for natural fruit abscission from spikelets), eventually leading to bunch rot and disease infection. As a fruit ripening agent, ethephon has been explored to hasten fruit abscission in many fruit crops and oil palm. Nevertheless, the previous studies in oil palm only focused on fruit shedding from FFB to improve oil extraction rate in oil mills without considering the actual FFB ripeness and retting period, which are critical for oil palm seed production. In this study, the application of ethephon containing buffer (adjusted to pH 9.0) to underripe FFB at 145 days after pollination (DAP), 135 DAP and 125 DAP resulted in 50% more fruit abscission after a 72-h incubation. Considering the minimal seed loss upon FFB harvest (<1%) and 50% reduction in retting period, underripe FFB at around 145 DAP was found to be optimum for seed production using ethephon treatment. The treatment, however, made negligible improvement in fruit detachment for ripe FFB at 150 DAP and older. Importantly, seed germination and culling rate at nursery stages were not significantly affected by the ethephon treatment. Hence, ethephon application can improve commercial seed production practices for oil palm.

Genomic Analysis and Secondary Metabolites Production of the Endophytic Bacillus velezensis Bvel1: A Biocontrol Agent against Botrytis cinerea Causing Bunch Rot in Post-Harvest Table Grapes

Botrytis bunch rot caused by Botrytis cinerea is one of the most economically significant post-harvest diseases of grapes. In the present study, we showed that the bacterial strain Bvel1 is phylogenetically affiliated to Bacillus velezensis species. The strain Bvel1 and its secreted metabolites exerted an antifungal activity, under in vitro conditions, against B. cinerea. UHPLC–HRMS chemical analysis revealed that iturin A2, surfactin-C13 and -C15, oxydifficidin, bacillibactin, L-dihydroanticapsin, and azelaic acid were among the metabolites secreted by Bvel1. Treatment of wounded grape berries with Bacillus sp. Bvel1 cell culture was effective for controlling grey mold ingress and expansion in vivo. The effectiveness of this biological control agent was a function of the cell culture concentration of the antagonist applied, while preventive treatment proved to be more effective compared to curative. The strain Bvel1 exhibited an adequate colonization efficiency in wounded grapes. The whole-genome phylogeny, combined with ANI and dDDH analyses, provided compelling evidence that the strain Bvel1 should be taxonomically classified as Bacillus velezensis. Genome mining approaches showed that the strain Bvel1 harbors 13 antimicrobial biosynthetic gene clusters, including iturin A, fengycin, surfactin, bacilysin, difficidin, bacillaene, and bacillibactin. The results provide new insights into the understanding of the endophytic Bacillus velezensis Bvel1 biocontrol mechanism against post-harvest fungal pathogens, including bunch rot disease in grape berries.

Effects of mechanical thinning on botrytis bunch rot on Sauvignon blanc wine grapes

Mechanical fruit thinning could be a practical and cost-effective alternative to hand thinning of Sauvignon blanc grapes to increase quality by reducing yield. Botrytis bunch rot, caused by the fungus Botrytis cinerea, is the main seasonal disease risk for grapes grown in New Zealand but it is unknown if this disease is exacerbated by mechanical rather than manual thinning of the vines. It was hypothesised that the damage caused by mechanical thinning would result in more disease or increase disease pressure than hand thinning or no thinning. Botrytis bunch rot was determined in the field at harvest following mechanical thinning in the 2009, 2010 and 2011 seasons compared with an un-thinned control. In the 2011 season, possible mechanisms that may have influenced disease severity were investigated. The parameters investigated were: bunch openness; berry susceptibility to infection; and percentage of bunch debris infected with Botrytis cinerea. Mechanical thinning resulted in the same or lower observed disease severity compared with the un-thinned control in the 2009, 2010 and 2011 seasons while reducing yield as desired. In all seasons, both heavy and light machine thinning treatments reduced incidence of botrytis compared to the un-thinned control and the heavy machine treatment always reduced disease severity compared to the un-thinned control. Berry susceptibility to Botrytis cinerea was a complex interaction between various factors. Heavy machine thinned berries without wounding and inoculation were significantly less susceptible than the un-thinned control. Further investigation will be required to determine if the significant differences observed in berry susceptibility to infection and total infected bunch debris per bunch can be correlated with observed field disease levels.

Varietal Response to Sour Bunch Rot in Polish Grapevine Genetic Resources

The aim of this study was to assess the resistance to sour rot of twenty-eight valuable cultivars of grapevine for wine production and twenty-five cultivars of table grapevine with diverse geographic and genetic origins, and to explain the causes of varied resistance based on the features related to the morphology, biology and ecology of assessed genotypes. The study was conducted for six years in the grapevine field collection of the National Institute of Horticultural Research in Skierniewice (Poland, latitude 51.9627 N, longitude 20.1666 E). Sour rot was severe in three seasons with abundant rainfall during the berry ripening stage. The number of wine and table cultivars in particular classes of resistance (mean value for three years) was as follows: very little or little—9 (wine) and 9 (table), medium—9 (wine) and 3 (table), high or very high—10 (wine) and 13 (table). The severity of bunch sour rot was positively correlated with single berry weight (moderate or weak correlation), bunch density and single bunch weight (very weak or weak correlation), and negatively correlated with thickness of berry skin (strong correlation) and the time of the beginning of veraison (weak correlation). Cultivars that were characterized by such agrobiological and ecological features as easy detachment of the berry from the pedicel, sensitivity to berry skin cracking, frequent damage to the skin by insects, and sensitivity to sunburn, were more heavily exposed to sour rot.

Disease Susceptibility of Interspecific Cold-Hardy Grape Cultivars in Northeastern U.S.A

Susceptibility to diseases of economically important grapes is critical to the evaluation of germplasm recommended for commercial production and for the development of sustainable production systems. In 2018–2019, the cold-hardy grape cultivars including ‘Brianna’, ‘Crimson Pearl’, ‘Itasca’, ‘Louise Swenson’, ‘Marechal Foch’, ‘Marquette’ ‘Petite Pearl’, ‘St. Pepin’, and ‘Verona’ were evaluated on non-treated vines for susceptibility to downy mildew, powdery mildew, black rot, anthracnose, Phomopsis leaf spot and fruit rot, and Botrytis bunch rot. No cultivars were consistently disease-free, and all exhibited some degree of black rot and powdery mildew infection. Relative susceptibility to disease was not consistent across both years, but ‘Brianna’ had greater incidence of black rot and ‘Louise Swenson’ showed lower incidence of powdery mildew in both years. The relatively new cultivars ‘Crimson Pearl’ and ‘Verona’ exhibited comparatively moderate disease susceptibility overall. Growers typically manage diseases with fungicides on commercial farms, so cultivar susceptibility is just one component of a sustainable pest management and production system.

Diffusible Compounds Produced by Hanseniaspora osmophila and Gluconobacter cerinus Help to Control the Causal Agents of Gray Rot and Summer Bunch Rot of Table Grapes

Gray and summer bunch rot are important diseases of table grapes due to the high economic and environmental cost of their control with synthetic fungicides. The ability to produce antifungal compounds against the causal agents Botrytis, Aspergillus, Penicillium, and Rhizopus of two microorganisms isolated from table grapes and identified as Hanseniaspora osmophila and Gluconobacter cerinus was evaluated. In dual cultures, both biocontrol agents (together and separately) inhibited in vitro mycelial growth of these pathogens. To identify the compounds responsible for the inhibitory effect, extractions were carried out with organic solvents from biocontrol agents separately. Through dual cultures with pathogens and pure extracts, only the hexane extract from H. osmophila showed an inhibitory effect against Botrytis cinerea. To further identify these compounds, the direct bioautography technique was used. This technique made it possible to determine the band displaying antifungal activity at Rf = 0.05–0.2. The compounds present in this band were identified by GC-MS and compared to the NIST library. The most abundant compounds, not previously reported, corresponded to alkanes, ketones, alcohols, and terpenoids. H. osmophila and G. cerinus have the potential to control the causal agents of gray and summer bunch rot of table grapes.

Disease Susceptibility of Interspecific Cold-hardy Grape Cultivars in Northeastern U.S.A.

Susceptibility to economically-important diseases of grapes is critical to the evaluation of germplasm recommended for commercial production and for development of sustainable production systems. In 2018-2019, nine cold-hardy grape cultivars including &lsquo;Brianna&rsquo;, &lsquo;Crimson Pearl&rsquo;, &lsquo;Itasca&rsquo;, &lsquo;Louise Swenson&rsquo;, &lsquo;Marechal Foch&rsquo;, &lsquo;Marquette&rsquo; &lsquo;Petite Pearl&rsquo;, &lsquo;St. Pepin&rsquo;, and &lsquo;Verona&rsquo; were evaluated on non-treated vines for susceptibility to downy mildew, powdery mildew, black rot, anthracnose, Phomopsis leaf spot and fruit rot, and Botrytis bunch rot. No cultivars were consistently disease-free, and all exhibited some degree of black rot and powdery mildew infection. Relative susceptibility to disease was not consistent across both years, but &lsquo;Brianna&rsquo; had greater incidence of black rot and &lsquo;Louise Swenson&rsquo; showed lower incidence of powdery mildew in both years. The relatively new cultivars &lsquo;Crimson Pearl&rsquo; and &lsquo;Verona&rsquo; exhibited comparatively moderate disease susceptibility overall. Growers typically manage diseases with fungicides on commercial farms, so cultivar susceptibility is just one component of a sustainable pest management and production system.

Volatile Organic Compounds (VOCs) Produced by Gluconobacter cerinus and Hanseniaspora osmophila Displaying Control Effect against Table Grape-Rot Pathogens

Table grapes (Vitis vinifera) are affected by botrytis bunch rot and summer bunch rot, the latter a complex disease caused by Botrytis cinerea, Aspergillus spp., Penicillium expansum and Rhizopus stolonifer. To search for biocontrol alternatives, a new bioproduct composed of Gluconobacter cerinus and Hanseniaspora osmophila, a consortium called PUCV-VBL, was developed for the control of fungal rots in table grapes. Since this consortium presents new biocontrol species, the effect of their VOCs (volatile organic compounds) was evaluated under in vitro and in vivo conditions. The VOCs produced by the PUCV-VBL consortium showed the highest mycelial inhibition against Botrytis cinerea (86%). Furthermore, H. osmophila was able to inhibit sporulation of A. tubingensis and P. expansum. VOCs’ effect in vivo was evaluated using berries from Red Globe, Thompson Seedless and Crimson Seedless grapes cultivars, demonstrating a mycelial inhibition by VOCs greater than 70% for all evaluated fungal species. The VOC identification of the PUCV-VBL consortium was analyzed by solid-phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GCMS). A total 26 compounds were identified, including 1-butanol 3-methyl, propanoic acid ethyl ester, ethyl acetate, phenylethyl alcohol, isobutyl acetate and hexanoic acid ethyl ester. Our results show that VOCs are an important mode of action of the PUCV-VBL biological consortium.

Response of Tannat (Vitis vinifera L.) to pre-flowering leaf removal in a humid climate

The aim of this study was to test the effect of pre-flowering leaf removal (PFD) on grape sanitary status, yield, source-sink balance and berry composition. A completely random block design experiment was conducted over four seasons in a commercial vineyard of the Tannat/SO4 combination located in the south of Uruguay (34° 35´30 S, 56° 15´23 O). The PFD treatment was compared with a commercial defoliation (CC) comprising partial leaf removal between the fruit set and cluster closure stages (four leaves from the first node), a traditional practice carried out by winegrowers. Both treatments received equal phytosanitary management during the study. The results were conditioned by seasonal meteorological conditions, particularly rainfall, temperature and evapotranspiration. The seasonal effect was significant for yield components, berry composition and source-sink balance. The PFD treatment resulted in the lowest yields in all four years and modified the primary and secondary composition of berries. It also showed a higher anthocyanin potential in 2016, 2017 and 2019, related to a higher percentage of exposed clusters, lower yield and/or higher leaf to fruit ratio. In 2017, environmental conditions were more favourable for the development of bunch rot, and lower values of incidence (3 %) were recorded for the PFD treatment compared to CC (22 %), due to greater exposure of bunches and less compact bunches. The PFD vines showed a steady reduction in dry matter production capacity, mainly explained by the steady reduction in yields. The Tannat variety showed a differential response to PFD depending on the weather during the growth cycle. Under humid climate conditions, pre-flowering defoliation proved to be effective for yield control, by reducing bunch rot incidence, and for improving some attributes in terms of grape composition. This work provides useful information for grape growers in humid regions on how to improve the sanitary status and quality of their production.