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Fire blight, caused by Erwinia amylovora, is a severe disease of pear (Pyrus communis). Highly vigorous trees are more sensitive to E. amylovora damage after summer pruning. Trees grown in high-density orchards have lower vigour than those in low-density orchards, reducing required inputs for pruning and tying, and increasing per hectare yields orchard profitability. Tree damage due to fire blight was assessed in high-density pear orchards vs. the common Israeli low-density orchards. Pear trees were planted at high densities using the spindle system (2500 trees ha-1 for ‘Spadona’ and 1250 trees ha-1 for ‘Coscia’), or at low density (1000 trees ha-1) using palmeta (’Spadona’) or open vase (‘Coscia’) systems. Four years after planting, both orchards were similarly infected with fire blight (11–50 infected blossoms per tree), but 1 year after infection, trees in the high density orchard had blossoms infections in the main limbs or trunk bases compared to the low-density orchard. At 3 years after initial infection, no trees had died in the high density orchard, whereas in the low density ‘Spadona’ orchard, 10% of the trees were wilted. For the more tolerant ‘Coscia’, infection did not progress at either orchard density. These results indicate that in fire blight-susceptible pear cultivars, a high density planting system, associated with reduced tree vigour, presents a decreased risk of fire blight damage.

The lychee fruit is in high demand worldwide. However, the yields of many cultivars are low, including the high-quality cultivars “Nuomici” (NMC) and ”Fei Zi Xiao” (FZX), which are very tasty and produce large fruit with a small seed, but tend to shed their fruitlets. In a previous work, we found that cross-hand pollination of “Mauritius” (MA) with pollen of another cultivar increased fruit set and reduced fruit-drop in comparison to self-hand pollination. In the current research, we aimed to identify the optimal pollen donor for three of the main cultivars grown in Israel: MA, FZX, and “Tamuz” (TA). We compared the effect of different pollinizers and found that the Vietnamese cultivar “Hong Long” (HL), which is becoming an important cultivar in Israel, was the optimal pollinizer for the three cultivars. In addition, we found that FZX and TA were not self-fertile under the Israeli environmental conditions since they tend to shed fruitlets that originated from self-fertilization. In contrast, MA is able to fertilize itself, although cross-pollination greatly increased its fruit number and size. We also identified a new PCR marker for lychee, M3, that enabled us to distinguish between self- and cross-fertilized FZX fruits pollinated by HL. Our results indicate that cross-pollination, particularly by HL, has beneficial effects on the production of lychee and it is especially important for cultivars that generate small seeds and tend to shed their fruitlets.

Chemical thinning of apple fruitlets is an important practice as it reduces the natural fruit load and, therefore, increases the size of the final fruit for commercial markets. In apples, one chemical thinner used is Metamitron, which is sold as the commercial product Brevis® (Adama, Ashdod, Israel). This thinner inhibits the electron transfer between Photosystem II and Quinone-b within light reactions of photosynthesis. In this study, we investigated the responses of two apple cultivars—Golden Delicious and Top Red—and photosynthetic light reactions after administration of Brevis®. The analysis revealed that the presence of the inhibitor affects both cultivars’ energetic status. The kinetics of the photoprotective mechanism’s sub-processes are attenuated in both cultivars, but this seems more severe in the Top Red cultivar. State transitions of the antenna and Photosystem II repair cycle are decreased substantially when the Metamitron concentration is above 0.6% in the Top Red cultivar but not in the Golden Delicious cultivar. These attenuations result from a biased absorbed energy distribution between photochemistry and photoprotection pathways in the two cultivars. We suggest that Metamitron inadvertently interacts with photoprotective mechanism-related enzymes in chloroplasts of apple tree leaves. Specifically, we hypothesize that it may interact with the kinases responsible for the induction of state transitions and the Photosystem II repair cycle.

Pollination is limiting for avocado production. We examined whether adding bumblebees (BBs; ca. 10 hives/ha) to conventional honeybees (HB; 5 hives/ha) would improve ‘Hass’ avocado pollination and yields. A preliminary trial (2017/18) in an avocado orchard with four consecutive rows of ‘Hass’ followed by one row of ‘Ettinger’ serving as a pollenizer (20% ‘Ettinger’) showed a considerable increase in ‘Hass’ yield in rows adjacent to (up to 80 m from) the BB hives vs. distant rows (=controls). In 2018/19, the trials were extended to three additional orchards. A significant yield increase was obtained in the BB hive-adjacent trees compared to BB hive-distant ones. Similar results were obtained in 2019/20, in experiments conducted throughout the country. The SNP analysis, to determine the parents of ‘Hass’ fruit at varying distances from the BB hives, showed no differences in the cross-pollination rate (‘Hass’ × ‘Ettinger’). However, pollination rates and the number of germinating pollen grains per stigma decreased with distance from the hives, and correlated to the negative gradient in yield. Taken together, our data suggest that adding BB hives to ‘Hass’ avocado orchards, at ca. 10 hives/ha resulting in 0.5–1.0 BB visits/tree per min, increases pollination and, accordingly, total yield.