Morphological and Molecular Description of Phytophthora insolita Isolated from Citrus Orchard in India

Citrus, an important cash crop in India, is adversely affected by Phytophthora nicotianae, P. palmivora, and P. citrophthora. Phytophthora insolita is known to be associated with citrus and reported for the first time in India. It is a rare and poorly characterized Phytophthora species, as its natural host and pathogenic impact are unclear. Previously, it was reported only in Taiwan and China; so to confirm our suspected isolate is P. insolita, regions of internal transcribed spacer, elongation factor, beta-tubulin, and cytochrome oxidase genes were sequenced. This study provides description of the lone Indian P. insolita isolate with respect to molecular identity, morphology, mating behaviour, and pathogenicity. 1. Introduction Phytophthora species (Greek-plant destroyer) are important plant pathogens, formerly thought to be fungus but its closest widely known relatives are brown algae and diatoms [1]. It is a representative of kingdom Chromalveolata, phylum Heterokontophyta, and class Oomycota. It affects almost every cultivated or forest vegetation. Phytophthora persists mainly in the soil as “chlamydospores” and spreads generally by asexual spores called “zoospores”; both of them are capable of infection by developing mycelia and parasitizing the host, but the latter is more potent. Citrus is an important tropical crop, cultivated in nearly 135 countries, and is vulnerable to more than 100 diseases and disorders [2]. Phytophthora induced diseases, however, cause enormous damage and economic losses in citrus production. There are 12 Phytophthora species known to infect citrus worldwide, namely, P. boehmeriae, P. cactorum, P. capsici, P. cinnamomi, P. citricola, P. citrophthora, P. drechsleri, P. hibernalis, P. megasperma, P. palmivora, P. nicotianae, and P. syringe [3]. There are reports of other associated Phytophthora species, like P. insolita and P. humicola, isolated from soil in a citrus orchard [4]. In India, P. nicotianae, P. palmivora, and P. citrophthora are major citrus pathogens [5, 6]. Recently we have reported P. insolita from India for the first time, which was isolated from Nagpur mandarin (Citrus reticulata) orchard [7]. P. insolita was reported for the first time from citrus soil in Changhua, Taiwan [4]. The species was noticed in southern China’s Hainan Island [8] and Ohio, USA (from necrotic Rhododendron leaf) [9]. The species remains poorly described and characterized in the literature as compared to other Phytophthora species, which may be due to its infrequent isolation. Moreover, the pathological impact of this citrus