Physiological Performance of Asymptomatic and Yellow Leaf Syndrome‐affected Sugarcanes in Venezuela

Abstract

Serological analyses revealed the presence of the sugarcane yellow leaf virus (ScYLV) in asymptomatic (S–) and symptomatic (S+) yellow leaf syndrome‐affected sugarcane plants of the cultivars PR.692176, C.323–68, V.64–10, V.71–47, V.75–6, SP.72–2086, SP.72–1210, SP.74–2005, C.323–68, B.80–549 and B.82–363. Tests for the presence of the sugarcane yellows phytoplasma, carried out by Dr P. Jones (IACR‐Rothamsted), gave negative results in all cultivars. Physiological analyses were performed in the top visible dewlap (TVD) leaf of S– and S+ plants of the cultivar PR.692176. All plants were at the second ratoon and flowering. When compared with S– plants, the S+ plants showed: (a) a marked reduction in the area of the leaf and internodes; (b) a high accumulation of total reducing sugars (TRS), glucans and α‐amino‐N in the leaf blade and of TRS in the corresponding leaf sheath; (c) a decrease in the chlorophyll, phosphorus and nitrogen content in the leaf; (d) the disappearance of the leaf diurnal fluctuations in TRS accumulation and export as well as the daily oscillations of TRS and glucans between dawn and dusk; and (e) major ultrastructural alterations in the companion cells of the phloem, including the accumulation of ScYLV particles in the cytoplasm. In S– plants, none of the growth and physiological alterations described above were observed, in spite of the high density of ScYLV particles in the cytoplasm. The location of S– and S+ plants close to each other without a discernible pattern of distribution in plots subjected to optimal irrigation and fertilization rule out the possibility that environmental conditions underlay the appearance of symptoms. In plots under severe drought for 3 months, however, all S– plants become S+. Symptom expression did not affect the acid phosphatase activity in the rhizosphere of S+ plants.