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Smiljana Goreta, Kristina Batelja, and Slavko Perica

The effect of thinning to three, four, five, or six lateral shoots on the growth parameters of five differently colored poinsettia (Euphorbia pulcherrima) cultivars (‘Christmas Star’, ‘Christmas Feelings’, ‘Cortez Candy’, ‘Marble Star’, and ‘Primero Roso’) was studied by consecutive measurements of growth from September to December. In a separate experiment, the effect of pot size (13-, 15-, or 18-cm diameter) on growth of ‘Christmas Star’ was studied. Cultivars responded similarly to thinning, but during the growing season, apparent differences in vegetative growth parameters between cultivars were observed, with ‘Primero Roso’ evaluated as the most vigorous. At the single-shoot level, the increased number of lateral shoots decreased the number of nodes at the beginning and the stem diameter at the end of the experiment. Leaf area, dry weight of stems, and total plant weight increased as the number of laterals increased at the end of experiment. The most distinctive canopy attribute in this study was the bract color because, according to customer evaluation, significant differences in visual appearance among tested cultivars were observed only for that trait. Pot size differentially affected the vegetative growth parameters of poinsettia ‘Christmas Star’. Increasing pot size from a 13- to 18-cm diameter resulted in an increase of plant canopy diameter, stem diameter, and the number of nodes on lateral shoots. There were no other substantial benefits on the measured growth parameters that could justify the use of pots larger than a 13-cm diameter for a poinsettia crop established at the beginning of September.

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Smiljana Goreta, Slavko Perica, Gvozden Dumicic, Lovre Bucan, and Katja Zanic

Suggested watermelon planting densities and N rates vary on a large scale, indicating that there is insufficient knowledge about their effects. Therefore, the objective of this study was to evaluate the effects of N rate and planting density on growth, yield and quality of watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] grown on black polyethylene mulch. The field experiments with `Crimson Sweet' watermelon were conducted in two climatologically different growing regions. The treatments were factorial combinations of three in-row plant spacings (0.5, 1.0, and 1.5 m) and three N rates (115, 195, and 275 kg·ha-1). Part of the N (35 kg·ha-1) was applied preplant and the remainder was fertigated. Vine length increased linearly up to 7 weeks after planting (WAP) as N rate increased from 115 to 275 kg·ha-1, and up to 9 WAP as plant spacing increased from 0.5 to 1.5 m. Total and marketable yields per ha or per plant did not increase with N rates above 115 kg·ha-1. Average fruit weight and fruit size distribution were generally unaffected by N rate. Leaf N concentration increased as N rate increased, although leaf N concentrations at the lowest N rate (115 kg·ha-1) even at 9 WAP were relatively high (43.3 to 47.3 g·kg-1). Total and marketable yields per ha were linearly decreased with an increase in plant spacing from 0.5 to 1.5 m, and the same was noticed with the total and marketable number of fruit per ha. With increased plant spacing average fruit weight increased and fruit size distribution shifted to larger categories.

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Gabriela Vuletin Selak, Slavko Perica, Smiljana Goreta Ban, Mira Radunic, and Milan Poljak

Olive orchard productivity largely depends on the choice of planted cultivars and their pollination needs. Orchard designs in Croatia are changing because a number of valuable foreign olive cultivars, mostly Italian, have been introduced in this region in the last 30 years. The compatibility relationships of introduced cultivars with autochthonous cultivars are unknown. With the objective of studying reproductive behavior of the most important Croatian cultivars (Drobnica, Lastovka, Levantinka, and Oblica) and their cross-pollination to recently introduced Italian cultivars Leccino and Pendolino, initial and final fruit set in self-pollination versus cross-pollination and free pollination were compared during three flowering seasons. Experiments were conducted in three different orchards (Kastela, Mravince, and Brac) to identify the effect of the environment on reproductive behavior of olive cultivars. The differences of fruit set in five olive cultivars after tested pollination treatments appeared at the time of initial fruit set. Increased final fruit set under cross-pollinations was observed when compared with self-pollination for all olive cultivars in all experimental orchards. In the Mravince orchard, a positive response to cross-pollination was consistent, and fruit set increased under cross-pollination in all cultivars and years with the exception of ‘Levantinka’ in which no significant differences were noticed between self-pollination treatment and cross-pollination treatments in 2005. Variable self-fertility behavior from season to season was found for tested cultivars. A self-incompatibility index (ISI) higher than 0.1 was recorded for ‘Levantinka’ in all experimental years and, therefore, classified it as a partially self-incompatible cultivar. Self-incompatibility response was observed for ‘Lastovka’. The positive response to cross-pollination over self-pollination only in some experimental years classified ‘Drobnica’, ‘Leccino’, and ‘Oblica’ as partially self-incompatible. Results obtained from this study indicated that pollination efficiency is strictly combination-specific. The Italian cultivar, Leccino, was a successful pollen acceptor and pollenizer of most Croatian cultivars. Reciprocal high success in cross-pollination was recorded for ‘Levantinka’ and ‘Oblica’. In the Mravince orchard, ‘Lastovka’, ‘Leccino’, and ‘Oblica’ were efficient pollenizers of ‘Levantinka’ where the simultaneous flowering period was in accordance with their cross-compatibility. ‘Levantinka’ was a good pollenizer for ‘Lastovka’ in the Mravince orchard, and both cultivars entered into the flowering period earlier than other studied cultivars, which was not the case in the other two orchards. The variations in flowering timing among orchards were a consequence of differences in environmental conditions. According to the high fruit sets recorded in ‘Oblica’ after pollination with ‘Leccino’ or ‘Levantinka’, an increase in tree productivity of the acceptor cultivar is expected in the presence of selected pollenizers in all olive-growing regions.

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Slavko Perica, Nacer Bellaloui, Carl Greve, Hening Hu, and Patrick H. Brown

Boron (B) remobilization, mannitol and glucose concentrations, and the effect of B application on changes in soluble carbohydrates were investigated in various organs of bearing `Manzanillo' olive trees (Olea europaea L. `Manzanillo'). Following foliar 10B application to leaves of various ages, there was significant 10B export out of the treated leaves, and significant 10B enrichment in nontreated adjacent organs, including inflorescences and fruit. Results demonstrated that B can be remobilized from leaves of various ages, and that foliar-applied B is phloem mobile in olive. Soluble carbohydrate analysis determined that mannitol and glucose are the predominant sugars in all organs analyzed and that the mannitol concentration in the leaves is adequate to account for all B transport. This is consistent with observations in other species, where the presence of mannitol is known to facilitate phloem B transport through formation of a mannitol-B complex. Previous reports have indicated that B application can alter carbohydrate metabolism. In the present study, foliar B application significantly suppressed glucose concentration in the leaf petioles of all ages and increased mannitol in petioles of the current-year-developed leaves.

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Slavko Perica, Patrick H. Brown, Joseph H. Connell, Agnes M.S. Nyomora, Christos Dordas, Hening Hu, and James Stangoulis

A 2-year field study was conducted to determine if foliar B applications prior to flowering increased fruit set in olive (Olea europaea L.) cv. Manzanillo. Boron solutions were applied (935 L·ha-1) at four concentrations (0, 246, 491, and 737 mg·L-1) to trees exhibiting no vegetative symptoms of B deficiency. Foliar B application increased both the percentage of perfect flowers and fruit set, but no effect on pollen germination was observed in either year. The increase in fruit set was not accompanied by a reduction in fruit size. The beneficial effects of foliar B application varied between years and were greater when fruit set was low. The results obtained here are in agreement with those observed in other tree species, in which foliar B applications made immediately prior to flowering or during the period of floral bud initiation significantly increased fruit set and yield. The physiological basis for this effect, however, remains unclear.