A checklist of rust fungi from Himachal Pradesh, India

An updated analysis of the diversity of rust fungi in Himachal Pradesh is provided herein as a product of field surveys, of mycological analysis, and of all forms of published documentation and literature. The results of all forms of analysis revealed that Himachal Pradesh has 167 species of rust fungi belonging to the class Pucciniomycetes. The class is represented by 11 families, 23 genera with 167 species. The Pucciniaceae (96 species) followed by Phragmidiaceae (14 species) are the largest families of rust fungi reported from the state. Rest of the families were found associated with 1–10 species of rust fungi. The rust fungi (19 species) with uncertain placement are placed in incertae sedis. The rust genera reported from Himachal Pradesh so far are Aecidium, Chrysomyxa, Coleosporium, Frommea, Gymnosporangium, Kuehneola, Kweilingia, Melampsora, Monosporidium, Ochrospora, Peridermium, Phakopsora, Phragmidium, Pileolaria, Puccinia, Pucciniastrum, Pucciniostele, Ravenelia, Skierka, Uredinopsis, Uredo, Urocystis, and Uromyces.


INTRODUCTION
Rust fungi are highly specialized obligate plant parasites having several unique morphological and microscopic features. These fungi commonly appear as yellow orange or brown powder on a variety of host plants and plant parts. Unlike other plant pathogens, rusts usually affect healthy and vigorously growing plants; the infection is limited to plant parts, such as leaves, petioles, tender shoots, stem, and fruits. The group is considered as one of the most harmful plant pathogens in agriculture, horticulture and forestry. These fungi are of major concern because they act as limiting factors for the successful cultivation, plantation and growth of agricultural crops and forestry plants. A wider diversity and broader host range is exhibited by this fungal group and their infection is not only limited to agricultural crops but also non-agricultural plants including medicinal herbs, shrubs, trees, and even weeds. An estimated 168 rust genera and approximately 7,000 species exist on various plant hosts, more than half of which belong to the genus Puccinia (Mohanan 2010).
Rust fungi show unique systematic characteristics among all fungal groups. A single species may produce up to five morphologically and cytologically distinct spore-producing structures, viz., spermagonia, aecia, uredinia, telia, and basidia, in successive stages of reproduction during the infection process. The presence of these successive stages may vary from species to species. To initiate and develop infection, rusts require an average temperature up to 35°C along with 50-60 % relative humidity. The rust infected plants may appear stunted, chlorotic (yellowed), or otherwise discoloured, whereas, disease symptoms includes coloured pustules, witches brooms, stem canker, hypertrophy of the affected tissues or formation of galls (Cummins & Hiratsuka 2003). Unlike other fungi, rusts exhibit one of the most important characteristics of their exceptionally high degree of host specificity.
Among all reported rust fungi, some are among agriculture's most destructive and devastating pathogens, causing diseases such as wheat stem rust, wheat yellow (stripe) rust, Asian soybean rust, coffee rust and many more. These rust fungi cause annual crop losses in billions every year worldwide. This loss can be greater in developing world where growers are not aware about diseases caused by rust fungi and often cannot afford fungicides. Owing to their economic importance, the rusts have been studied extensively in regular mycological surveys in Himachal Pradesh, but no single-source compiled literature is available. Therefore, this study facilitates the access to scattered Himalayan literature with reference to rust fungi to the students and plant pathologists of national and international community.

STUDY AREA
Himachal Pradesh is one of the northern states of India that lies between 30.  East. It is a mountainous state with very high mountains to grasslands in plain ( Figure 1). Great variations in elevation ranging from about 350m (1,148 ft) to 7,000m (22,966 ft) are found in the state. The variations are also observed in the climatic conditions. Hot and sub-humid tropical conditions were found in the southern tracts while, cold, alpine and glacial conditions in the northern and eastern mountain ranges with more elevation. The variability in rainfall was observed in the range of 1,500-3,000 mm. These variations in geo-climatic conditions of the state lead to greater biodiversity in the state. A total 66.52% of the area is covered with very dense evergreen to deciduous forests types. While, alpine shrub and meadows are found distributed in the west and northeastern Himalaya; alders, birches, rhododendrons, and moist alpine shrubs are regional vegetation. The plant pathogens including bacteria, fungi and viruses are also found due to these changeable geographical and climatic conditions of the state which are quite favourable for their growth and development.

MATERIALS AND METHODS
The information on rust fungi was gathered by investigating the following data sources: (1) mycological survey conducted on rust fungi from Himachal Pradesh during the years 2014 to 2018, and (2) all forms of published documentation and literature (Bilgrami et al. 1991;Jamaluddin et al. 2004). The names of some taxon in the obtained data have been replaced by currently accepted names as they were of out-of-date. The current usage of names was checked using the Index Fungorum (http://www.indexfungorum.org/) to adopt the generic and specific taxonomy in Species Fungorum (http://www.speciesfungorum.org/). The plant samples found infected with rust fungi were collected during a mycological survey of various localities of Himachal Pradesh. Field observations of rust fungi on host plants and their photographs were taken in natural conditions. Collected specimens were packed in paper bags and taken to the laboratory for further analysis. A few disease samples were used for morphological analysis of the rust fungi and the rest of the materials were dried for future microscopic studies. The air dried specimens were preserved in standard size herbarium packets and deposited at the Abhilashi University Mycological Herbarium (AUMH).
The microscopic mounts were prepared from fresh samples by brushing the rust powder into a drop of distilled water and lactophenol on microscopic slides, which were covered with cover slip and gently heated. The microscopic slides were analysed for spore dimensions like size, shape and ornamentations.
Both macro-and micro-morphological characters obtained from the laboratory were only used for taxonomic studies of the collected fungi. The fungal specimens were identified and their distribution records were checked by using standard literature (Cummins & Hiratsuka 2003;Mukerji & Manoharachary 2010). Illustrations are photographed under microscope equipped with digital camera.

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(2 each). The rest of the plant species were reported to be infected with a single rust fungus. The area-wise results revealed that most of the rust fungi (about 127) were reported from Shimla and nearby regions followed by Solan (22) (Vasudeva 1958;Joshi & Merchand 1963;Mishra et al. 1965Mishra et al. , 1975Ahmad et al. 1969

DISCUSSION
The present study provides the checklist of rust fungi from Himachal Pradesh, a northwestern Himalayan State of India. A remarkable diversity of rust fungi have been reported from the state which has an area of 55,673km 2 . The state exhibits marked variations in climate and vegetation and so far in fungal diversity. The available information about rust fungi from the state is in general meager and there is much scope for exploratory work on the taxonomy, diversity and ecological aspects of these fungi. There are about 167 species, 23 genera belonging to 11 families recorded from this hilly Himalayan state, with great variations in host infected (about 171 plant species belonging to 121 genera and 52 families). This distinguished diversity of rust fungi may be due to the fact that rust fungi tend to prefer humid habitats, which is one of the major characteristic features of the state. Being obligate parasites, rust fungi are associated with spreading and development of nutrient plants and are found in many belts, both on herbaceous plants, and on trees and shrubs.
After compilation of literature it is observed that most of the rust fungi were reported from Shimla and nearby regions. Although, these fungi are also reported from other districts of the state but the scope of exploration of these fungi and their host range is still there.
Two checklists on two major rust genera namely, Puccinia (Gautam & Avasthi 2016b) Uromyces (Gautam & Avasthi 2017a) have recently been published from this hilly state. Two new species of rust fungi namely Puccinia himachalensis (Gautam & Avasthi 2016a) and Skierka himalayensis (Gautam & Avasthi 2017b) have been reported from the state which are new to science. Whereas, Pileolaria pistaciae (Gautam & Avasthi 2017b), Kweilingia divina (Gautam & Avasthi 2018) are the new additions to the mycobiota of the state while, Puccinia tiliaefolia (Gautam & Avasthi 2017c) has been rediscovered after 46 years from India. During the literature survey we did not come across any molecular studies conducted on rust fungi from the state. As per greater phytodiversity of the state, studies on the rust fungi are inadequate and there is vast scope to conduct studies and fill the data gaps. Molecular studies of rust fungi are still required besides morphological taxonomy, which will not only help in revision and reassessment of the existing fungal species, but also to find their correct taxonomic position. The knowledge generated by the work is of immense utility as it is a key to revealing the diversity and ecology of rust fungi from Himachal Pradesh Himalaya.