Reactive oxygen species are a byproduct of aerobic metabolic processes but are also produced by plants in defense against pathogens. In addition, they can function as signaling molecules that control various aspects of plant life, ranging from developmental processes to responses to abiotic and biotic stimuli. In plants, reactive oxygen species can be produced by respiratory burst oxidase homologues. Arabidopsis contains 10 genes for respiratory burst oxidase homologues that are involved in different aspects of plant life. Plant pathogenic cyst nematodes such as Heterodera schachtii induce a syncytium in the roots of host plants that becomes a feeding site which supplies nutrients throughout the life of the nematode. In line with this function, the transcriptome of the syncytium shows drastic changes. One of the genes that is most strongly downregulated in syncytia codes for respiratory burst oxidase homologue B. This gene is root-specific and we confirm here the downregulation in nematode feeding sites with a promoter::GUS (β-glucuronidase) line. Overexpression of this gene resulted in enhanced resistance against nematodes but also against leaf-infecting pathogens. Thus, respiratory burst oxidase homologue B has a role in resistance. The function of this gene is in contrast to respiratory burst oxidase homologues D and F, which have been found to be needed for full susceptibility of Arabidopsis to H. schachtii. However, our bioinformatic analysis did not find differences between these proteins that could account for the opposed function in the interaction with nematodes.

Arabidopsis contains 317 genes for defensin-like (DEFL) peptides. DEFLs have been grouped into different families based mainly on cysteine motifs. The DEFL0770 group contains seven genes, of which four are strongly expressed in roots. We found that the expression of these genes is downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii as revealed by RNAseq analysis. We have studied one gene of this group, At3g59930, in detail. A promoter::GUS line revealed that the gene is only expressed in roots but not in other plant organs. Infection of the GUS line with larvae of H. schachtii showed a strong downregulation of GUS expression in infection sites as early as 1 dpi, confirming the RNAseq data. The At3g59930 peptide had only weak antimicrobial activity against Botrytis cinerea. Overexpression lines had no enhanced resistance against this fungus but were more resistant to H. schachtii infection. Our data indicate that At3g59930 is involved in resistance to nematodes which is probably not due to direct nematicidal activity.

Arabidopsis contains 34 genes for glycosylphosphatidylinositol (GPI)-anchored LTPg proteins. A motif analysis has placed these into four groups. With one exception, all are produced with a signal peptide and are most likely attached to the cell membrane via the GPI anchor. Several of the LTPg genes across the four groups are downregulated in syncytia induced by the beet cyst nematode Heterodera schachtii. We have here studied At3g22600 encoding LTPg5, which is the most strongly downregulated LTPg gene. It is mainly expressed in roots, and a promoter::GUS line was used to confirm the downregulation in syncytia and also showed downregulation in galls of the root knot nematode Meloidogyne incognita. In contrast, infection with bacteria (Pseudomonas syringae) and fungi (Botrytis cinerea) led to the induction of the gene in leaves. This diverse regulation of LTPg5 indicated a role in resistance, which we confirmed with overexpression lines and a T-DNA mutant. The overexpression lines were more resistant to both nematode species and to P. syringae and B. cinerea, while a knock-out mutant was more susceptible to H. schachtii and P. syringae. Thus, LTPg5 encoded by At3g22600 is part of the Arabidopsis resistance mechanism against pathogens. LTPg5 has probably no direct antimicrobial activity but could perhaps act by associating with a receptor-like kinase, leading to the induction of defense genes such as PR1.

Upland cotton (Gossypium hirsutum L.) is the world’s leading fiber crop, and is considered the backbone of Pakistan’s national economy (Hamid et al. 2012). Bacterial leaf blight attributed to Xanth...

Spinach (Spinacia oleracea L.) is a cool-season annual plant native to countries in the southwestern and central regions of Asia. Alternaria alternata, the causal agent of Alternaria leaf spot, is a major constraint to spinach production worldwide. The objective of this study was to determine the relative efficacy of biological control agents (BCAs) under lab and field conditions. In vitro testing showed that Bacillus subtilis provided the greatest early inhibition (50.0% inhibition at 8 days). Trichoderma harzianum showed the most consistent antagonistic activity (29.67% inhibition at 12 days) when compared to the other BCAs. Based on consistent in vitro antagonistic performance, T. harzianum and B. subtilis were selected for evaluation under field conditions using a Randomized Complete Block Design (RCBD). The field trial showed that the treatment involving BCAs (T. harzianum + B. subtilis) resulted in significantly lower severity scores of 12.0%, representing a 65.7% reduction compared to the untreated control (35.2%). The T. harzianum + B. subtilis treatment also provided the greatest vigour in plant growth with higher fresh weight (27.30 g) and total dry weight (2.25 g). These improvements are likely associated with the known mycoparasitic activity of T. harzianum and the induction of plant defence responses by B. subtilis. The data support the idea that a combination of BCAs could be a viable, eco-friendly option for integrated management of Alternaria leaf spot in spinach production.

Guava (Psidium guajava L) is a widely cultivated fruit plant in tropical and subtropical countries, including Pakistan, where it is attacked by numerous pathogenic fungi. Guava stem cracking is caused by a destructive disease that significantly affects the stem and other parts of the plant. This study was conducted to isolate the causative pathogen of stem cracking and its management with chemicals and silver nanoparticles (AgNPs). Samples were obtained from seven different locations of Punjab, Pakistan, and the pathogen was isolated and purified on PDA using the hyphal tip technique. After the confirmation of pathogenicity, spore suspension was plated in a 96-well plate for chemical evaluation and a 9-day-old culture was used to find the AgNPs effect by the agar dilution method. Antifungal activity was measured in terms of optical density (OD) for chemicals and percent growth inhibition (PGI) for AgNPs. Four fungicides (Mancozeb, Iprodione, Chlorothalonil and Deconil) were evaluated at 7 different concentrations (50mg/ml, 25 mg/ml, 12.5 mg/ml, 6.25 mg/ml, 3.12 mg/ml, 1.56 mg/ml and 0.78 mg/ml) against P. psidii and the maximum antifungal effect was seen at the concentration of 50mg/ml. In vitro evaluation of fungicides showed Iprodione maximum spore growth inhibition against P. psidii. Silver nanoparticles were used to analyze their antifungal potential at different concentrations (1 ppm, 10 ppm, 100 ppm), whereas the maximum inhibition zone was seen at 100 ppm of AgNPs. Data was statistically analyzed by using factorial design under Complete Randomized Design (CRD). The outcomes of the present study revealed that using chemicals and silver nanoparticles can help to manage guava stem canker.