Footrot disease due to Nectria haematococca (anamorph Fusarium solani f. sp. pisi) is an economically important disease of peas globally. However, our ability to predict accurately the likelihood of footrot infections is limited because there is no method to determine inoculum density prior to planting. In this research, a PCR-based assay was developed to quantify the pea pathogenicity gene (PEP3), exclusive to highly pathogenic forms of N. haematococca, from DNA extracted from agricultural field soils. The applicability of using quantitative PCR (qPCR) to measure this gene in soil was validated, and the relationship between PEP3 gene numbers and footrot disease was also studied. Results showed that the quantitative assay is both efficient and specific; amplification efficiency of the Q-PCR assay for the PEP3 gene was 92. Gene copy numbers were shown to vary significantly (P= 0.01) between fields, and were positively correlated to the number of spores of pathogenic N. haematococca, and to footrot disease. PEP3 numbers of up to 100 g -1 soil constituted a threshold number for infection-potentially capable of causing economically significant pea footrot disease. The density of virulent N. haematococca in soil fields capable of causing footrot disease could be determined with a high degree of accuracy, with this assay. It offers the opportunity for prediction of pea footrot infections in agricultural soils prior to cultivation. © 2010 Springer Science+Business Media B.V

Aim:  The aim of this study was to develop molecular assays for investigating the presence and diversity of pathogenicity genes from the pea footrot pathogen Nectria haematococca (anamorph Fusarium solani f.sp. pisi) in soils. Methods and Results:  Polymerase chain reaction (PCR) assays were developed to amplify four N. haematococca pathogenicity genes (PDA, PEP1, PEP3 and PEP5) from isolates and soil‐DNA from five agricultural fields with a prior footrot history. A collection of 15 fungi isolated on medium selective for Fusarium spp. exhibited variation in their virulence to peas as assessed via a disease index (DI: 0–5; no virulence to the highest virulence). PCR analyses showed that three isolates in which all four pathogenicity genes were detected resulted in the highest DI (>3·88). All four pathogenicity genes were detected in soil‐DNA obtained from all five fields with a footrot disease history, but were not amplified from soils, which had no footrot history. Denaturing gradient gel electrophoresis and/or sequence analysis revealed diversity amongst the pathogenicity genes. Conclusion:  The PCR assays developed herein enable the specific detection of pathogenic N. haematococca in soils without recourse to culture. Significance and Impact of the Study:  Molecular assays that specifically target pathogenicity genes have the capacity to assess the presence of the footrot‐causing pathogen in agricultural soils.

Irvingia (bush mango) species are economically important trees, but studies aimed at their prospect for domestication did not take into account the potential differences between members of the Genus. Hence fruit size, postharvest pathology and phytochemicals of I. gabonensis and I. wombolu were studied. Results showed that whilst the mean weight, length, width and thickness of fruits of I. gabonensis were 125.08g, 60.85mm, 62.66mm and 56.78mm, respectively, those obtained from I. wombolu were 86.08g, 54.23mm, 54.09mm and 50.97mm, respectively. Difference in brownish-black rot fruit disease between the two Irvingia species was not significant (P=0.05), but disease severity increased correspondingly with increase in storage days. Four genera of fungi (Aspergillus, Penicillium, Rhizopus and Mucor) were isolated from fruits of both Irvingia species, and I. wombolu was found to sustain a significantly lower fungal population (7.76E+07 cfu) than I. gabonensis (1.05E+08 cfu). High fungal population led to a correspondingly high severity of brownish-black rot disease. Fruits of both Irvingia species possessed all five phytochemicals (alkaloids, flavonoids, saponins, tannins and glucosides). However, whilst both species had the same amounts of flavonoids and glycosides, I. wombolu possessed relatively higher amounts of alkaloids, saponins and tannins than I. gabonensis. I. wombolu may be the preferred choice if domestication would be based on phytochemicals. In like manner, I. gabonensis may be the preferred choice for domestication if taste, weight and size of fruits were the parameters of interest.

Seeds are the means of propagating about 90% of all food crops in the world, and they significantly influence yield potential in crop plants. Moreover, seeds are adversely affected by a number of factors such as postharvest and storage disease pathogens and unfavourable environmental conditions. Seed-borne pathogens represent a major threat to crop establishment and yield. Exposure of seeds to disease pathogens and other adverse conditions disrupts their normal physiology and metabolism which ultimately affects productivity. It is therefore imperative to promptly diagnose, treat, prevent and control seed related diseases. As with every other sphere of scientific studies, seed pathology has evolved tremendously over time; hence in this paper the development and emerging perspectives of this all important discipline was reviewed. Pathogen exclusion by detection and elimination of infested seed lots is required for disease management but traditional and conventional measures such as visual examination, use of media culture and serology are inadequate to detect pathogens associated with seed. In contrast, Nucleic acid-based molecular tools, such as the polymerase chain reaction (PCR) have emerged as faster and more reliable means for detecting and quantifying pathogens in seeds than conventional techniques.

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The use of culture-dependent methods in studying bacterial community has been proven to be inadequate, and often give misleading results. In this work, metagenomic analysis targeting the 16S ribosomal RNA genes was used to study the diversity and community structure of bacteria associated with postharvest Irvingia fruits. Results showed that Simpson's diversity indices and number of Operational Taxonomic Units were dependent on the storage period (days after harvest, DAH) of fruits. Fresh fruits assessed on the day of harvest (DAH = 0) had a Simpson's diversity index of 0.82, while fruits assessed on the 3 rd and 6 th DAH had diversity indices of 0.69 and 0.72, respectively. Whilst fruits assessed on the day of harvest had 64 OTUs spanning across 7 phyla, 11 Classes, 32 genera with total reads of 23,776, fruits assessed on the 3 rd and 6 th days after harvest had 58 OTUs spanning across 6 phyla, 9 Classes, 30 genera with 20,949 reads and 66 OTUs spanning across 4 phyla, 6 Classes, 33 genera with 30,722 reads, respectively. Results further showed that majority of the OTUs belonged to two phyla -Proteobacteria and Firmicutes, mostly represented by members of Alphaproteobacteria and Bacilli subdivisions respectively. Predominant among these OTUs were sequences belonging to Acetobacter ghanensis (11.94%), A. okinawensis (15.36%), Lactobacillus species (14.90%), L. collinoides (12.35%), L. plantarum (7.11%) and L. vaccinostercus (2.89%). The relative abundance of these microorganisms indicates that fleshy pericarp of Irvingia fruits hitherto treated as wastes could potentially be used as a substrate in food and pharmaceutical industries.

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The use of harvested chewing sticks after prolonged storage period is therefore not advisable for oral hygiene measures.