Dynamics of adaptive responses in growth and resistance of rubber tree clones under South American leaf blight non-escape conditions in the Colombian Amazon

Abstract

Rubber trees (Hevea brasiliensis) in Latin America are strongly affected by a disease known as South American Leaf Blight (SALB), which is caused by the foliar fungus Microcyclus ulei, renamed Pseudocercospora ulei. This study analyzed the temporal dynamics (eight years) of growth and resistance to SALB in nine promising American clones and the IAN 873 clone (control) during the immature phase in large-scale clone trials, using models for longitudinal data and GGE biplot analyses as a measurement of their specific adaptation to climatic conditions in a SALB non-escape zone in the Colombian Amazon. High averages of monthly precipitation (>300 mm), temperature (>25.2 °C), relative humidity (>88%) and dew point (>23 °C) were recorded in the years with a high incidence of SALB. After 8 years, the better clones (FDR 5788, FDR 5597, FX 4098 and GU 198) blended the desirable characteristics pre-tapping vigour (CMT > 40 cm), foliar retention (FRL ≤ 1 or ≥79% of leaves retained) and partial resistance to SALB (low severity, AT1 and AT2 had scores <2 and low conidial and ascosporic sporulation, TR had scores <4, and ST had scores <2), which indicated an adaptive advantage over SALB’s high pressure agro-climatic conditions, contrary to that observed in clones IAN 873 (control), CDC 56 and FX 3899 P1. Finally, these clones need to be analyzed in terms of their productive performance before making a valid recommendation to producers.