The pecan (Carya illinoinensis) industry in South Africa is growing rapidly, and it is becoming increasingly crucial to understand the risks posed to pecans by fungal pathogens. Black spots on leaves, shoots, and nuts in shucks caused by Alternaria species have been observed since 2014 in the Hartswater region of the Northern Cape Province of South Africa. Species of Alternaria include some of the most ubiquitous plant pathogens on earth. The aim of this study was to use molecular techniques to identify the causative agents of Alternaria black spot and seedling wilt isolated from major South African pecan-production areas. Symptomatic and non-symptomatic pecan plant organs (leaves, shoots, and nuts-in-shucks) were collected from pecan orchards, representing the six major production regions in South Africa. Thirty Alternaria isolates were retrieved from the sampled tissues using Potato Dextrose Agar (PDA) culture media and molecular identification was conducted. The phylogeny of multi-locus DNA sequences of Gapdh, Rpb2, Tef1, and Alt a 1 genes revealed that the isolates were all members of Alternaria alternata sensu stricto, forming part of the Alternaria alternata species complex. The virulence of six A. alternata isolates were tested on detached nuts of Wichita and Ukulinga cultivars, respectively, as well as detached leaves of Wichita. The A. alternata isolates were also evaluated for their ability to cause seedling wilt in Wichita. The results differed significantly between wounded and unwounded nuts of both cultivars, but not between the cultivars. Similarly, the disease lesions on the wounded detached leaves were significantly different in size from the unwounded leaves. The seedling tests confirmed that A. alternata is pathogenic and that A. alternata causes black spot disease and seedling wilt of pecans. This study is one of the first documentations of Alternaria black spot disease of pecan trees and its widespread occurrence in South Africa.

Black spot disease or Alternaria black spot (ABS) of pecan (Carya illinoinensis) in South Africa is caused by Alternaria alternata. This fungal pathogen impedes the development of pecan trees and leads to low yield in pecan nut production. The present study investigated the in vitro effect of six fungicides against the mycelial growth of A. alternata isolates from ABS symptoms. Fungicides tested include Tilt (propiconazole), Ortiva (azoxystrobin), AgTin (fentin hydroxide), and Bellis (boscalid + pyraclostrobin). All fungicides were applied in 3 concentrations (0.2, 1, and 5 μg mL−1). Tilt and Bumper 250 EC containing propiconazole active ingredient (demethylation Inhibitors) were the most effective and inhibited all mycelial growth from up to 6 days post-incubation. The other active ingredients (succinate dehydrogenase inhibitors, organotin compounds, and quinone outside inhibitors) showed 75–85% mycelial growth inhibition. The effective concentration to inhibit mycelial growth by 50% (EC50) was estimated for each isolate and fungicide. The overall mean EC50 values for each fungicide on the six isolates were 1.90 μg mL−1 (Tilt), 1.86 μg mL−1 (Ortiva), 1.53 μg mL−1 (AgTin), and 1.57 μg mL−1 for (Bellis). This initial screening suggested that propiconazole fungicide was the most effective for future field trials test and how these fungicides could be used in controlling ABS disease.

Alternaria black spot disease on pecan is caused by the opportunistic pathogen Alternaria alternata and poses a serious threat to the local South African and global pecan industry. Several diagnostic molecular marker applications have been established and used in the screening of various fungal diseases worldwide. The present study investigated the potential for polymorphism within samples of A. alternata isolates obtained from eight different geographical locations in South Africa. Pecan (Carya illinoinensis) leaves, shoots, and nuts-in-shuck with Alternaria black spot disease were sampled, and 222 A. alternata isolates were retrieved. For rapid screening to identify Alternaria black spot pathogens, polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis of the Alternaria major allergen (Alt a1) gene region was used, followed by the digestion of the amplicons with HaeIII and HinfI endonucleases. The assay resulted in five (HaeIII) and two (HinfI) band patterns. Unique banding patterns from the two endonucleases showed the best profile and isolates were grouped into six clusters using a UPGMA (unweighted pair group method with arithmetic averages) distance matrix (Euclidean) dendrogram method on R-Studio. The analysis confirmed that the genetic diversity of A. alternata does not depend on host tissues or the pecan cultivation region. The grouping of selected isolates was confirmed by DNA sequence analysis. The Alt a1 phylogeny corroborated no speciation within the dendrogram groups and showed 98–100% bootstrap similarity. This study reports the first documented rapid and reliable technique for routine screening identification of pathogens causing Alternaria black spot in South Africa.

Antimicrobial resistance to typical antibiotics is a significant threat to human health worldwide, and its rapid progression have raised serious concern in the treatment of infectious diseases. The cost of commercialising a new antibiotic is high relative to a low return on investment. Medicinal plants are used for the treatment of infections in many countries and are customarily recognised in Africa. Many studies have shown that phytochemicals produced by plants have exerted potential antimicrobial activities against pathogens through various action mechanisms. However, crude extracts from medicinal plants may be an alternative source of antimicrobial resistance modifying agents because of the large range of bioactive compounds. This systematic review aims to assess published articles in Africa on medicinal plants with potential antimicrobial resistant effectives, focusing on bacterial and fungal microbes. To assess this studies, bibliometric model on Scopus and Web of Science databases were used to systematically search for “Antimicrobial Activity’ or “Medicinal Plants” as titles for studies published from 1980 to 2019 in Africa. We identified a total of 2,174 published documents retrieved from 710 sources between 1980 to 2019, and there was an increasing trend of publications over the years. A stringent selection process was established based on clear inclusion and exclusion criteria, yielding 138 data of the most represented medicinal plants, grouped by family and species names. A total of 52 bacterial and 27 fungi were generated in these studies. Egypt, Nigeria, and South Africa were the most represented single and multiple countries with publication, and highest citation counts. In terms of country, Egypt and South Africa had the highest collaborative strength. Most relevant research of 43 articles were published in the Journal of Heterocyclic Chemistry, with Victor Kuete as the 20th most productive author. Natural Product Research was least Journal with 17 published articles. This systematic review study depicts the progression of antimicrobial resistant studies from medicinal plants in Africa and the noticeable research outcomes at current. The study also provided perspectives for future research, pharmaceutical companies, policy makers, research funders, policy makers, and researchers.

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