A mutant peach (Prunus persica Batsch) cultivar 'Shimizu Hakuto RS', developed by radiation breeding, shows the same quality as the original cultivar, 'Shimizu Hakuto'. However, it shows poorer fruit set than the parent strains. The fruit set of this cultivar only reaches 20 to 30% of the total numbers of flower; whereas the original one reached 50 to 70%. As a result of morphological observation, the higher ratio of morphological abnormalities in pistils, slowing degeneration or incomplete development of the ovary and embryo sac, causes poor fruit set. Furthermore, the numbers of normal pollen per anther were smaller in 'Shimizu Hakuto RS' than in the parent strains. We suggest that this number reduces the probability of pollination and thus results in lower percentages of ovule fertilization. Nevertheless, the poor fruit set did not cause lower fruit productivity. We find it is a very labor-saving variety because the labor hours for flower or fruit thinning from March to May were remarkably reduced.
This study investigated the real-time diagnosis of potassium concentration in 'Muscat of Alexandria' grapes grown in a soilless culture system using perlite medium. Potassium concentration in the squeezed sap of the petiole was investigated at different growth stages. Its relations to the severity of leaf injury attributable to potassium deficiency at stage III of fruit growth and fruit quality were assessed. Potassium concentration lower than 500 mg・L −1 in sap at veraison engenders a higher correlation between the potassium level and leaf scald severity. These signs are more severe in plants with lower potassium concentrations. There were no such signs when potassium concentrations in the sap greater than 500 mg・L −1 . At 1000 mg・ L −1 or lower potassium concentration in the sap at veraison, a positive relationship was also observed between the potassium level and berry size. Berry size was smaller when the potassium level in the sap was less than 1000 mg・L −1 . Even when the potassium concentration was 4000 mg・L −1 , an extremely low sugar content, implying a lower commercial value, was not observed. Relationships between potassium concentrations in the sap at the berry set stage and leaf scald or fruit quality were not clearer than those at the veraison stage.
We examined the effects of summer fertilization and pruning on nitrogen levels in the bleeding sap and petioles of 'Muscat of Alexandria' grape vines under forcing culture from December. In the summer of 1999, 9 vines under soilless-culture were treated with combinations of 3 different fertilization levels with 3 pruning procedures. The effects of the summer fertilization and pruning on inorganic nitrogen levels in the bleeding sap were not clear. The summer fertilization affected the nitrate nitrogen levels in the petioles at the berry set stage in the subsequent season, since the levels of nitrate nitrogen in 10 gN・m −2 (10 g nitrogen application・m −2 ) and 15 gN・m −2 were higher than that in 5 gN・m −2 in the previous summer. The effect of summer fertilization on the inorganic nitrogen level was marked in the berry set stage; however, the difference in nitrogen levels among the fertilization treatments became indistinct at veraison. The summer pruning also affected the nitrogen levels in the petioles, since the levels of nitrogen in the vines pruned the previous summer were higher than the levels in those that did not undergo summer pruning. However, the severity of winter pruning did not affect the nitrogen levels in the petioles at any of the sampling times.
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