Histological Insights into Alternaria brassicae Infection in Brassica napus and Raphanus brassica | InformativeBD

Jawadayn Talib Alkooranee, from the different institute of Iraq. wrote a Reseach Article about, Histological Insights into Alternaria brassicae Infection in Brassica napus and Raphanus brassica. Entitled, Histological study of leaves symptoms of Brassica napus and Raphanus brassica infected by Alternaria brassicae. This research paper published by the International Journal of Agronomy and Agricultural Research (IJAAR). an open access scholarly research journal on Agronomy. under the affiliation of the International Network For Natural Sciences| INNSpub. an open access multidisciplinary research journal publisher.

Abstract

Alternaria leaf spot can be a devastating disease as the mechanism by which the fungus Alternaria brassicae (Berk.) Sacc.  spread in canola is not yet fully  understood. It is essential to understand the infection process and mechanisms of resistance by studying biotic and abiotic factors. In the present study, two abiotic elicitors-Salicylic acid (200 ppm), and Milor MZ (Mancozeb 64% + Metalaxyl 8% WP) fungicide (100 ppm) along with the biotic elicitor Pseudomonas fluorescens (PF83), were examined to induce systemic resistance in Brassica napus AACC (2n=38) and Raphanus brassica AARR (2n=38) against Alternaria leaf spot disease. The histological study revealed that R. brassica exhibited resistance to Alternaria leaf spot disease. Fungal colonies were observed on R. brassica leaves at 120 hours post-inoculation (hpi), and Similar observations were seen on B. napus leaves after 24 hpi. However, signs of the pathogen, including hyphae, conidia, appresoria, and dead cells, were present on the surface of the infected leaf in both genotypes but were not observed in plants treated with biotic and abiotic elicitors. Thus, the biotic elicitors PF83 and the abiotic elicitors SA and Milor MZ significantly reduced (P≤0.5) lesion sizes of pathogen at 24, 84, and 120 hpi in both genotypes. Finally, the results suggested that R. brassica produced resistance to Alternaria leaf spot. Additionally, the application of PF83 isolate is considered a useful tool for enhancing protection methods for canola genotypes.

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Introduction

The Brassicaceae family is economically and industrially significant, including many species important for oil production. Brassica napus is one of the top three most valuable oilseed crops, serving as a source of nutrition for humans, forage for animal feed, and raw material for biofuels and soil conditioners. It also holds significant socioeconomic importance across various industries (Borges et al., 2023). 

Alternaria brassica is a plant pathogenic fungus and the causal agent of Alternaria leaf spot disease. This disease can severely impact crops in the Brassicaceae family, including rapeseed (B. napus) and mustard (B. juncea), causing significant economic losses. In some cases, such as in Lithuania, it has caused 100% losses of seed yield (Brazauskiene and Petraitiene, 2006), while in Canada, losses have reached up to 42% (Degenhardt et al., 1974).

In general, A. brassicae infests the phyllosphere, causing early foliar deterioration, defoliation, and a reduction in the photosynthetic area (Sharma et al., 2002). Moreover, it reduces seed size, yield, and color, leading to a decrease in oil content (Kaushik et al., 1984). The hyphal growth of A. brassicola within the leaf tissues of B. oleracea results in the loss of host cell integrity and organelle disintegration at different levels (Macioszek et al., 2020). While many methods are available to control Alternaria leaf spot disease, they are not always effective (Meena et al., 2010). One of these methods involves using resistance-inducing factors such as Elicitor factors.

Elicitor factors that induce systemic resistance in plants are classified as biotic or abiotic, and as physical or chemical, depending on their origin and molecular structure. External elicitors can be defined as factors that influence the cellular system to build certain compounds involved in defense mechanisms against plant pathogens (Riseh and Vazvani, 2024). Bacteria that colonize plant roots and promote growth are referred to as plant growth-promoting rhizobacteria (PGPR). PGPR influences plant growth in two different ways: directly or indirectly. Nonpathogenic Pseudomonas species, a well-known genus for PGPR, are recognized for their antagonistic effects and their impact to stimulate induced systemic resistance (ISR) in plants. This enhances the effectiveness of bio-control strategies, contributing to improved cropping systems (Yu et al., 2022).

To identify the genome (AA, CC or RR) containing the resistance trait against Alternaria leaf spot disease, the researcher studied two genotypes: B. napus (AACC, 2n=36) and B. rapa/R. sativus (AARR, 2n = 38). Additionally, a comparative study, between biotic and abiotic elicitors, was conducted to induce systemic resistance in genotypes tested against Alternaria leaf spot.

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Source : Histological study of leaves symptoms of Brassica napus and Raphanus brassica infected by Alternaria brassicae