Intensity of the citrus variegated chlorosis in the state of Sao Paulo and South of Triangulo Mineiro

• Author(s): Ayres, Antonio; Barbosa, Jose; Gimenes-Fernandes, Nelson;
• Abstract: The intensity of the Citrus Variegated Chlorosis (CVC) was studied in commercial groves in the states of Sao Paulo and Minas Gerais (southwestern area) from 1996 to 1999. Four surveys were made with the three most important varieties of sweet oranges (Pera Rio, Valencia and Natal). A random stratified sampling was used, with samples proportional to the size of the strata. The following stratified factors considered were: variety, zone and plant age. The surveys took place in 1996, 1997, 1998 and 1999, respectively in 7,037; 6,491; 2,968 and 444 plants, proportionally distributed in the strata. To estimate the fruit yield losses, fruits from all sample trees were harvested, counted, weighed and then classified according to their diameter as normal (5 cm) or affected (5 cm). The percentage of CVC-affected trees for each factor (variety, zone and plant age) was estimated and an increase in disease incidence from 22.36% in 1996 to 36.52% in 1999 was observed. The plants with symptoms restricted to leaves (grade 1) were the most prevalent, ranging from 13.57% to 23.23%. The percentages for infection in grade 2 plants (plants with only one branch with symptoms in fruits and leaves) and in grade 3 plants (plants with generalized symptoms in fruits and leaves) were 4.96% to 13.97% and 1.11% to 2.15%, respectively. The North and Northwest regions showed in 1999 the highest disease incidence (55.38% and 47.61%, respectively). In this regions the highest rates of relative increase of CVC intensity were observed. The Center region showed an intermediate value of incidence (32.23% in 1999), and in the South a decrease of CVC was observed (22.14% to 14.74%). Plants of intermediate ages (3-5 years and 6-10 years) showed the highest intensity of disease. No difference among the varieties in relation to the CVC incidence and severity was detected. The total weight of fruits and the number of normal fruits in trees classified in grades 2 and 3 of CVC symptoms were statistically lower than those of healthy plants (grade 0). For grade 3 plants, the estimated average reduction was 74.98% in fruit weight and 70.87% in the number of normal fruits.
• Publication Date: May 2001
• Journal: Summa Phytopathologica