Ca-metalosate as an alternative Ca formulation for decreasing Ca related disorders in fruit trees

[摘要] ENGLISH ABSTRACT: Generally, calcium (Ca) foliar applications are used to improve the Ca status of fruit and control the incidence of Ca-related disorders, viz. bitter pit (BP) in apples and albedo breakdown (AB) in citrus. The main aim of the study was to determine whether Ca-metalosate as an alternative Ca formulation is effective in decreasing Ca-related disorders in fruit trees.Firstly, the role of formulation of Ca and boron (B) foliar applications to improve fruit quality in 'Golden Delicious' apples was quantified. Secondly, evaluation of pre-harvest foliar applications of a chelated Ca and B combination to reduce AB in citrus was carried out. Thirdly, xylem functionality in developing fruitlets of different apple cultivars was determined, as it impacts on Ca transport into the fruit.Ca concentration of fruit 80 days after full bloom (dafb), was significantly increased by Ca nitrate [Ca(NO3)2] foliar applications compared to Ca-metalosate and the control. The incidence of BP was also significantly reduced by Ca(NO2)3 foliar applications compared to the control, but not compared to Ca-metalosate. Results indicated that Ca foliar applications with a nitrate carrier, higher Ca concentration (active), lower point of deliquescence and molecular weight/size are more effective at increasing Ca concentration of fruitlets and reduce BP incidence in 'Golden Delicious' apples. This confirms previous findings that formulation has an effect on the efficiency and penetration of Ca foliar applications.B-metalosate in combination with Ca-metalosate failed to significantly reduce the incidence of AB in both sweet orange cultivars (Turkey and Cara Cara). Further research under South-African conditions, with an amended protocol, including five or more Ca-metalosate foliar applications, starting from 81 dafb, is suggested to determine if metalosates can successfully reduce the incidence of AB. This protocol differs from the one used in this study, but was successful when applied as salt formulation foliar application. Ca-metalosate and control indicated lower Ca (%) in the albedo tissue of creased fruit compared to non-creased fruit, indicating that Ca plays a role in AB.At ±49 dafb, a steady decline in xylem functionality was observed in all six apple cultivars evaluated, supporting recommendations that additional Ca foliar applications should start before 40 dafb to decrease the incidence of Ca-related disorders in fruit trees. Less susceptible apple cultivars showed an earlier decline of xylem functionality (42 dafb) compared to susceptible apple cultivars (49 dafb). This is in contrast to previous findings. A relationship between Ca-related disorders and loss of xylem functionality early in the season could not be established in this trial. A slight recovery of xylem functionality in all six apple cultivars evaluated was observed later in the season, under both climatic areas and this has not been reported previously in apples.Further research on xylem functionality under South African conditions should continue. Studies should commence earlier, starting at 28 dafb, and continue until harvest, to determine whether apple cultivars experiencing an earlier loss of xylem functionality are more prone to Ca-related disorders and whether xylem functionality slightly increases later in the season. By including microscopy studies during this period, the physical disruption of xylem bundles should be confirmed.

[发布机构] Stellenbosch University