ABSTRACT
An increase in temperature and extreme heat stress is responsible for the global reduction in maize yield. Heat stress affects the integrity of the plasma membrane functioning of mitochondria and chloroplast, which further results in the over-accumulation of reactive oxygen species. The activation of a signal cascade subsequently induces the transcription of heat shock proteins. The denaturation and accumulation of misfolded or unfolded proteins generate cell toxicity, leading to death. Therefore, developing maize cultivars with significant heat tolerance is urgently required. Despite the explored molecular mechanism underlying heat stress response in some plant species, the precise genetic engineering of maize is required to develop high heat-tolerant varieties. Several agronomic management practices, such as soil and nutrient management, plantation rate, timing, crop rotation, and irrigation, are beneficial along with the advanced molecular strategies to counter the elevated heat stress experienced by maize. This review summarizes heat stress sensing, induction of signaling cascade, symptoms, heat stress-related genes, the molecular feature of maize response, and approaches used in developing heat-tolerant maize varieties.
ABSTRACT
In August 2020 powdery mildew was observed on pear cv. Fertility at the University research field in Shalimar, Srinagar (J&K), India (34° 08' 30.5'' N and 74° 51' 42.0'' E) with a disease incidence up to 30% (100 leaves observed from ten trees). White irregularly shaped fungal colonies were observed on the abaxial leaf surface which latter covered the whole leaf surface and developed black chasmothecia. The affected leaves appeared brittle, slightly curved upwards and dropped prematurely. Mycelium was hypophyllous, septate and measured 2.0 to 5.0 µm in width. Appressoria were nipple shaped, solitary or present in opposite pairs. Conidiophores were erect, up to 440.0 µm long (n=50), mostly centrally on upper surface of mother cells. Conidiophore foot-cells were filiform, followed by 1 to 3 shorter cells, producing single conidia at the tip. Conidia were hyaline, lanceolate, with a non-papillate rounded apex, measuring55.5 to 81.4 × 14.8 to 22.5 µm (n=50) and devoid of any conspicuous fibrosin bodies. Germ tube was, filiform, twisted, arose basally and measured 2.0 to 5.0 µm in width. Chasmothecia were hypophyllous, black, scattered, globose and measured 195.0 to 255.0 µm in diameter (n=50) having 8 to 12 equatorial, acicular, up to 270.0 µm length appendages with 25.9 to 44.4 µm diameter bulbous base (n=50) and obtuse or subacute apex. Asci in a chasmothecium were clavate to saccate, 62.9 to 81.4 × 18.5 to 22.2 µm (n=50), stalked, and two- spored. Ascospores were 33.3 to 40.7 × 12.9 to 18.5 µm (n=50), pale yellowish or golden brown in color. All morphological features were consistent with Phyllactinia pyri-serotinae (Braun and Cook 2012). To confirm the fungus identity at molecular level, DNA of two isolates was extracted from chasmothecia. The internal transcribed spacer (ITS) sequence of ribosomal DNA was amplified with the primers ITS1 and ITS4 (White et al. 1990) and sequenced. The ITS sequences submitted to NCBI GenBank under Accession No. MZ505441 and MZ505442 have 97 (416/427) & 96 (424/440) per cent and 99 (424/430) & 98 (428/438) per cent base pair matching, with that of P. pyri-serotinae isolates from Japan (AB080521 and AB985507), respectively. Thus, the pathogen was identified as Phyllactinia pyri-serotinae Sawada based on morphological and molecular sequence analyses. The pathogenicity tests of both the isolates were carried out on one year old pear saplings (cv. Fertility) and repeated twice. The inoculum was prepared by collecting P. pyri-serotinae conidia in sterile distilled water from infected pear leaves. Three saplings were inoculated by spraying (15ml per sapling) the inoculum (3 x 105 spores ml-1) on leaf surfaces, while same number of saplings sprayed with sterile distilled water served as non-inoculated controls. After 15 days of incubation at 25oC in a green house, similar symptoms as observed on naturally infected plants were observed on inoculated plants and uninoculated plants remained symptomless. The pathogen of interest observed on inoculated plants was morphologically characterized and found to be similar to P. pyri-serotinae. The voucher specimen was deposited in the Herbarium Crytogamae Indiae Orientalis (HCIO), IARI, New Delhi under accession number 52213. Pear is the third most important temperate fruit grown in India (Chattopadhyay 2009) and our study reveal P. pyri-serotinae as the new causal agent of powdery mildew in addition to P. guttata (Dhar and Shah 1982) under Indian conditions.
ABSTRACT
Maize, a C4 sub-tropical crop, possesses higher temperature optima as compared to the C3 plants. Low temperature (LT) stress confines the growth and productivity of maize. In this context, two maize genotypes, LT tolerant Gurez local and LT susceptible Gujarat-Maize-6 (G-M-6) were analysed in present study for various osmolytes and gene expression of antioxidant enzymes including Ascorbate-glutathione (AsA-GSH) besides trehalose biosynthetic pathways. With the progressive LT treatment, Gurez local showed lesser accumulation of stress markers like hydrogen peroxide (H2O2) and malondialdehyde, a significant increase in osmoprotectants like free proline, total protein, total soluble sugars, trehalose, total phenolics and glycine betaine, and a significant reduction in the plant pigments as compared to the G-M-6. Additionally, Gurez local was found to possess a well-established antioxidant defense system as revealed from the elevated transcripts and enzyme activities of various enzymes of AsA-GSH pathway. Higher gene expression and enzyme activities were exhibited by superoxide dismutase, catalase and peroxidase besides the gene expression of trehalose biosynthetic pathway enzymes. Moreover, through principal component analyses, a positive correlation of all analysed parameters with the LT tolerance was noticed in Gurez local alone demarcating the genotypes on the basis of their extent of LT tolerance. Overall, the present study forms the basis for unravelling of LT tolerance mechanisms and improvement in the performance of the temperate maize. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01020-3.
