Abiotic stresses are one of the major constraints to crop production and food security worldwide. The situation has aggravated due to the drastic and rapid changes in global climate. Heat and drought stress are undoubtedly the two most important stresses having huge impact on growth and productivity of the crops. It is very important to understand the physiological, biochemical and ecological interventions related to these stresses for better management. A wide range of plant responses to these stresses could be generalized into morphological, physiological and biochemical responses. Interestingly, this review provides a detailed account of plant responses to heat and drought stresses with special focus on highlighting the commonalities and differences. Crop growth and yields are negatively affected by sub-optimal water supply and abnormal temperatures due to physical damages, physiological disruptions and biochemical changes. Both these stresses have multi-lateral impacts and therefore, complex in mechanistic action. A better understanding of plant responses to these stresses has pragmatic implication for remedies and management. A comprehensive account of conventional as well as modern approaches to deal with heat and drought stresses have also been presented here. A side-by-side critical discussion on salient responses and management strategies for these two important abiotic stresses provides a unique insight into the phenomena. A holistic approach taking into account the different management options to deal with heat and drought stress simultaneously could be a win-win approach in future.

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Crop Production under Drought and Heat Stress: Plant Responses and Management Options

Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic fungal pathogen causing disease in a wide range of plants. This review summarizes current knowledge of mechanisms employed by the fungus to parasitize its host with emphasis on biology, physiology and molecular aspects of pathogenicity. In addition, current tools for research and strategies to combat S. sclerotiorum are discussed. Taxonomy: Sclerotinia sclerotiorum (Lib.) de Bary: kingdom Fungi, phylum Ascomycota, class Discomycetes, order Helotiales, family Sclerotiniaceae, genus Sclerotinia. Identification: Hyphae are hyaline, septate, branched and multinucleate. Mycelium may appear white to tan in culture and in planta. No asexual conidia are produced. Long-term survival is mediated through the sclerotium; a pigmented, multi-hyphal structure that can remain viable over long periods of time under unfavourable conditions for growth. Sclerotia can germinate to produce mycelia or apothecia depending on environmental conditions. Apothecia produce ascospores, which are the primary means of infection in most host plants. Host range: S. sclerotiorum is capable of colonizing over 400 plant species found worldwide. The majority of these species are dicotyledonous, although a number of agriculturally significant monocotyledonous plants are also hosts. Disease symptoms: Leaves usually have water-soaked lesions that expand rapidly and move down the petiole into the stem. Infected stems of some species will first develop dark lesions whereas the initial indication in other hosts is the appearance of water-soaked stem lesions. Lesions usually develop into necrotic tissues that subsequently develop patches of fluffy white mycelium, often with sclerotia, which is the most obvious sign of plants infected with S. sclerotiorum.

Sclerotinia sclerotiorum (Lib.) de Bary: biology and molecular traits of a cosmopolitan pathogen.

Inducing drought tolerance in plants: Recent advances

The Colletotrichum acutatum species complex

Chalcone synthase (CHS, EC 2.3.1.74) is a key enzyme of the flavonoid/isoflavonoid biosynthesis pathway. Besides being part of the plant developmental program the CHS gene expression is induced in plants under stress conditions such as UV light, bacterial or fungal infection. CHS expression causes accumulation of flavonoid and isoflavonoid phytoalexins and is involved in the salicylic acid defense pathway. This review will discuss CHS and its function in plant resistance.

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Chalcone synthase and its functions in plant resistance

Fusarium head blight (FHB) or scab of wheat (Triticum aestivum L.) and its associated mycotoxin deoxynivalenol (DON) can cause devastating economic losses. In North America, FHB of wheat is caused mainly by Fusarium graminearum Schwabe [sexual stage Gibberella zeae (Schwein.) Petch]. In this study, the chemotype of 73 single-spore isolates of F. graminearum obtained from wheat kernels collected from 2007 to 2010 from FHB-affected fields and grain elevators in Nebraska was determined to be 15-ADON. Eight selected isolates were evaluated for aggressiveness on spikes and DON production in grain using the FHB-susceptible spring wheat cultivar ‘Wheaton’. Aggressiveness was quantified as disease severity and area under the disease progress curve (AUDPC). Disease severity at 21 days after inoculation ranged from 40.9% to 99.5% and AUDPC ranged from 284%-days to 1279%-days. DON production in grain, measured by enzyme-linked immunosorbent assay (ELISA), ranged from 0.2 to 11.0 µg g−1. Aggressiveness as mea...

Chemotype and aggressiveness of isolates of Fusarium graminearum causing head blight of wheat in Nebraska

ADDITIONAL INDEX WORDS. potting medium, disease suppressive properties, soilborne SUMMARY. Experiments conducted in vitro showed that coir [coconut (Cocos nucifera) mesocarp pith] suppressed growth of soilborne plant pathogens. Mycelial growth of Phytophthora capsici on potato dextrose agar (PDA) amended with an unsterilized coir suspension was strongly inhibited regardless of suspension concentration. Growth of P. capsici on PDA amended with a filter-sterilized coir suspension was uninhibited. Growth of Fusarium solani on water agar (WA) amended with unautoclaved coir was completely inhibited. Growth of F. solani on WA amended with autoclaved coir was uninhibited. Aspergillus terreus recovered from coir inhibited mycelial growth of various soilborne pathogens by up to 75%. The results from this study suggest that coir has the ability to suppress soilborne plant pathogens in vitro and this ability is largely due to microorganisms associated with the substrate.

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In Vitro Suppression of Soilborne Plant Pathogens by Coir

Stem rust caused by Puccinia graminis f. sp. tritici is one of the most destructive diseases of wheat (Triticum aestivum). In Afghanistan, wheat is an economically important crop, comprising approximately 80% of grain production. Little work has been done to identify Afghan wheat cultivars that are potential sources of stem rust resistance. Five modern Afghan wheat cultivars and 500 wheat accessions from Afghanistan and three adjacent regions in Pakistan, Iran, and Tajikistan were screened at the seedling stage for resistance to stem rust race TPMK. Four of the five modern Afghan cultivars (‘Hazardana’, ‘Kabul-2000’, ‘Solh-02’, and ‘Zardana’) displayed infection type 2 and were considered resistant. The four resistant lines were further evaluated at the Cereal Disease Laboratory (CDL), St. Paul, Minnesota, for resistance to seven stem rust races including TPMK (for confirmation) and TTKS (Ug99). All four lines were susceptible to race TTKS. However, ‘Hazardana’ and ‘Zardana’ were resistant to races QFCS, ...

Frequency of resistance to stem rust race TPMK in Afghan wheat cultivars

Characterization of Nebraska Isolates of Fusarium graminearum Causing Head Blight of Wheat

Wheat (Triticum spp.) stem rust, caused by Puc cinia graminis f. sp. tritici Eriks. and E. Henn. (Pgt), re-emerged as a devastating disease of wheat because of virulent race Ug99 (TTKSK). Many bread wheat ( T. aestivum L.) cultivars grown in North America are susceptible to Ug99 or its derivative races that carry additional viru lence. ‘Gage’ was released in 1963 mainly for its excellent field resistance to leaf rust (caused by Puccinia triticina Eriks) and stem rust. However, Gage’s resistance has not been genetically char acterized, which would facilitate its use in breed ing programs. To better define the nature of the resistance in Gage, we created an F 2 population and the corresponding F 2:3 and F 4:5 families from crosses between Gage and stem rust suscep tible cultivar ‘Bill Brown’. Inheritance of resis tance to Pgt race QFCSC and molecular marker analysis indicated that Sr2 and additional genes explain the stem rust resistance of Gage. Using seedling plant infection types from the F 2 , F 2:3 ,

Stephen N. Wegulo

Papers

Chemotype and aggressiveness of isolates of Fusarium graminearum causing head blight of wheat in Nebraska

In Vitro Suppression of Soilborne Plant Pathogens by Coir

Frequency of resistance to stem rust race TPMK in Afghan wheat cultivars

Characterization of Nebraska Isolates of Fusarium graminearum Causing Head Blight of Wheat

Characterization of Stem Rust Resistance in Wheat Cultivar Gage