Nimbya alternantherae reported for the first time to cause leaf and stem necrosis of Alternanthera philoxeroides (alligatorweed) in Pakistan

Abstract

A severe leaf and stem necrosis disease of Alternanthera philoxeroides (alligatorweed) was examined in the summer of 2011. Symptoms on leaves and stems of A. philoxeroides consisted of round to oval straw colored spots with maroon margins resulting in chlorosis, severe defoliation and withering of stems. The causal pathogen isolated on V-8 agar medium was morphologically identified as Nimbya alternantherae. Pathogenicity of N. alternantherae was proven on healthy A. philoxeroides plants. This is the first report of A. philoxeroides necrosis caused by N. alternantherae in Pakistan.

Polyalthia Longifolia a New Host Record of Nigrospora Sphaerica Causing Leaf Blight in Pakistan and Efficacy Determination of Various Fungicides Against This Pathogen

“…After 10 days, conidia were harvested by applying sterilized deionized water (containing 0.01% Tween 20) and gently scraping the culture surface with a microscopic glass slide. The conidial suspension was filtered through a 0.5 mm2 pore strainer to remove mycelia debris (Akhtar et al, 2011;2012). The resulting spore suspension was adjusted to 106 conidia per ml using a 59. haemocytometer (Farr and Rossman, 2010).…”

Spatial and temporal variability of the Alligatorweed pathogen, Alternaria alternantherae, in Louisiana

“…As an indicator of accumulated damage at the time of our sampling, we quantified the number of missing leaves per plant. Leafabscission may occur in response to high damage levels (Akhtar et al 2012, Faeth et al 1981, Gilbert et al 2005; thus, an examination of the proportion of missing leaves could be a fair representation of previously sustained damage. We calculated this fraction by subtracting the number of missing leaves from the total number of potential leaves (with 2 per node), then dividing by the total number of potential leaves and subtracting the result from 1.…”

“…2 Despite its known presence in the US since the 1970s, and numerous reports from around the world (Akhtar et al 2012, Barreto and Torres 1999, Gilbert et al 2005, field dynamics of A. alternantherae, and especially interactions with introduced biological control agents (e.g., Alligatorweed Flea Beetle), remain unstudied. In other systems, insect-fungal interactions range from positive (e.g., infection facilitates herbivory or vice versa) to negative (e.g., infection increases plant resistance to herbivory or decreases palatability; Saikkonen et al 1998), to both (e.g., herbivory reduces infection, but infection increases palatability to herbivores; Saikkonen et al 1998).…”