Calcium and potassium contents in nutrient solution on Phoma leaf spot intensity in coffee seedlings

ABSTRACT Coffee is one of the main export commodities of Brazilian agribusiness. Phoma leaf spot [Phoma tarda (Stewart) Boerema & Bollen] is one of the most important coffee fungal diseases in Brazil. Therefore, this study aimed to evaluate the intensity of Phoma leaf spot in coffee seedlings supplied with different rates of Ca+2 and K+. The study was conducted under controlled conditions in a growth chamber, at the Department of Phytopathology - UFLA, from February 2010 to December 2011. The assay was repeated twice under the same conditions. The nutrient solutions consisted of five concentrations of K+ (3, 4, 5, 6, 7 mmol L-1) and Ca+2 (2, 4, 6, 8 and 10 mmol L-1). The experiment was arranged in a randomized block design, with 25 treatments and three replicates, with two plants per plot. The areas under incidence progress curve (AUIPC) and severity (AUSPC) were calculated. At the lowest rate of Ca2+ (2 mmol L-1) and highest K+ (6 and 7 mmol L-1), approximately, the AUIPC was the smallest. For the AUSPC, the lowest rates of Ca+2 and K+ resulted in the lowest severities. Supply of Ca+2 and K+ in nutrient solution reduced AUIPC and AUSPC of Phoma leaf spot, and these nutrients can be recommended for the management of the disease.

摘要：咖啡是巴西农业综合企业的主要出口商品之一。由迟生茎点霉（Phoma tarda (Stewart) Boerema & Bollen）引发的茎点霉叶斑病（Phoma leaf spot）是巴西境内最具危害性的咖啡真菌病害之一。本研究旨在评估施加不同浓度钙离子（Ca²+）与钾离子（K+）的营养液对咖啡幼苗茎点霉叶斑病发病强度的影响。试验于2010年2月至2011年12月在巴西拉夫拉斯联邦大学（UFLA）植物病理学系的可控环境生长箱内开展，且在相同试验条件下重复两次。试验所用营养液设置了5个钾离子浓度梯度（3、4、5、6、7 mmol·L⁻¹）与5个钙离子浓度梯度（2、4、6、8、10 mmol·L⁻¹），试验采用随机区组设计，共包含25个处理组，设置3次重复，每小区种植2株咖啡幼苗。本研究计算了发病率进展曲线下面积（AUIPC）与严重度进展曲线下面积（AUSPC）两项指标。结果显示，当钙离子浓度最低（2 mmol·L⁻¹）且钾离子浓度处于最高梯度（约6和7 mmol·L⁻¹）时，AUIPC数值最小；而就AUSPC而言，钙离子与钾离子浓度均最低的处理组，其病害严重度最低。综上，在营养液中添加钙离子与钾离子可降低咖啡茎点霉叶斑病的AUIPC与AUSPC，因此可将这两种养分推荐用于该病害的防控管理。