Godwin R.A. Mchau

Phylogenetic analysis of Alternaria spp. associated with apple core rot and citrus black rot in South Africa

Dry core rot of apple (DCR) and Alternaria black rot of citrus (ABR) have in the past respectively been ascribed to Alternaria alternata and A. citri. In recent years, however, it has been speculated that several other species of Alternaria could also be associated with these diseases. In an attempt to elucidate the identity of these taxa, 25 isolates associated with DCR, and 26 isolates associated with ABR were selected for molecular characterisation. Nucleotide sequences of 1116 sites including the histone gene section and the internal transcribed spacers (ITS 1 and 2) of the rRNA gene were determined for these isolates. The gene trees generated from the individual and combined data sets using maximum parsimony, maximum likelihood and neighbour-joining analysis methods distinguished five clades with strong bootstrap support, namely Alternaria sp., A. arborescens, A. infectoria, A. tenuissima, and a clade containing isolates variable in morphology, referred to as the Alternaria group. In the alignment of the combined ITS and histone data set, unique transition/transversion substitutions, as well as positional insertions and deletions were observed for each of the above clades. In addition, key sequences in the form of serial composing nucleotides in both the ITS and histone sections of the alignment were also discovered for the molecular identification of A. arborescens, A. infectoria and A. tenuissima. The final phylogeny also indicated that no host specificity existed among the species associated with these two post-harvest disease complexes. Contrary to the host specificity observed on leaf diseases of these hosts in the field, it appears that the post-harvest diseases are the result of adverse storage conditions and opportunism of different small-spored Alternaria spp.

Isozyme diversity in Phytophthora palmivora: evidence for a southeast Asian Centre of origin

Isozyme and morphological data were obtained for 93 isolates of P. palmivora and six described as P. arecae . Sporangial shape for both species ranged from spherical to ellipsoid with a high percentage of sporangia predominantly ellipsoid with a broad base and a short occluded pedicel less than 5 m in length. Fourteen enzymes stained in starch gels yielding 17 putative loci, 11 of which were monomorphic, the remainder being polymorphic (GPI, HEX2, IDH1, MDH1, PEP and SOD). Phosphoglucose isomerase (GPI) and isocitric dehydrogenase (IDH1) were the most variable loci. Isozyme analysis of the 99 isolates revealed 18 electrophoretic types (ETs). Isolates of P. arecae clustered with P. palmivora in ET7 and ET8, the most common ETs found in P. palmivora . Considerable genetic diversity was found amongst P. palmivora isolates from coconut ( Cocos nucifera ) with 8 ETs, durian ( Durio zibethinus ) with 5 ETs and other non-cacao hosts from Indonesia, Malaysia, Philippines and Thailand. Since coconut and durian are indigenous to the region, a southeast Asian origin for P. palmivora seems probable. Finally, since no significant differences were found in either morphology or isozymes between isolates of P. palmivora and P. arecae , this study provides definitive evidence that the two species are conspecific.

An integrated study of morphological and isozyme patterns found within a worldwide collection of Phytophthora citrophthora and a redescription of the species

A worldwide collection of 77 isolates of Phytophthora citrophthora from 30 different host species was investigated for variation in morphology and isozyme patterns. All isolates produced non-caducous, papillate sporangia. Only those isolated from cacao ( Theobroma cacao ) in Brazil produced chlamydospores, whereas cacao isolates from Indonesia did not produce chlamydospores. Over 70% of the isolates were sterile; the remainder could be designated as the A2 mating type based on pairings with P. capsici , though P. citrophthora itself did not produce oospores. The species was separated into three distinct isozyme subgroups: CTR1 containing isolates from widely distributed geographical locations on a broad range of hosts, CTR2 composed exclusively of Brazilian isolates from cacao, and a new subgroup CTR3 consisting of Indonesian isolates also isolated from cacao. A total of 14 enzymes and 17 putative loci were used to compare the isolates and seven loci were polymorphic. Peptidase was diagnostic for CTR1, malate dehydrogenase (MDH1) for CTR2 while the migration patterns for both glucose-6-phosphate dehydrogenase and hexokinase (HEX2) differentiated CTR3. A redescription of R. citrophthora is presented based on all 77 isolates including physiological, morphological and isozyme characters that can assist identification.

Effect of organic acid pretreatment on some physical, functional and antioxidant properties of flour obtained from three unripe banana cultivars

Unripe banana flour (UBF) obtained from organic acid pretreatment of pulp from three non-commercial cultivars were profiled for physical, functional and antioxidant properties. UBF showed marked significant differences (p<0.05) in colour (CIEL(∗)a(∗)b(∗) and CIELCH) and water holding capacity with no significant difference in oil holding capacity. The total polyphenol content (TPC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) differed significantly with M-red UBF recording high TPC (1130.39 ± 27.26 mg GAE/100g d.w.) at 10 g/L citric acid pretreatment. Correlation analysis between TPC and DPPH showed very strong positive correlation for Mabonde UBF in citric and lactic acid pretreatment (r = 0.999, p < 0.01; r = 0.985, p < 0.01), while inverse correlation was recorded in M-red UBF for ascorbic and lactic acid pretreatment (r = -0.031; r = -0.137). Organic acid pretreatment enhances the physical and antioxidant properties of UBF hitherto absent in composite food formulations.

Functional Properties and Postharvest Utilization of Commercial and Noncommercial Banana Cultivars

Banana (Musa spp.) is one of the worlds most important crops cultivated in tropical and subtropical regions of the world. Banana is a major source of macro-elements, especially potassium, and contains health-beneficial ingredients such as resistant starch, total dietary fibers, rapidly digestible starch, and slowly digestible starch. Oligosaccharides (fructooligosaccharides and inulin) and polyphenols ((+)-catechin, (-)-epicatechin, (-)-epigallocatechin, and gallic acid) are other ingredients present in bananas that have found application in the prevention of muscular contractions, regulation of blood pressure, prevention of colon cancer and diabetes, and in the cure of intestinal disorders when unripe. This review identifies the different commercial and noncommercial banana cultivars and their utilization. Commercial cultivars include Williams (M. acuminata cv. Williams), Dwarf Cavendish (M. acuminata cv. Petite Nain), Chinese Cavendish (M. acuminata cv. Chinese Cavendish), Grand Nain (M. acuminata cv. Grand Nain), and Goldfinger (M. acuminata cv. Goldfinger), with Mabounde and Luvhele identified as noncommercial varieties. Banana postharvest utilization includes its use as functional foods, prebiotics, probiotics, nutraceuticals, and processing into value-added products.

Morphological, physicochemical, and antioxidant profile of noncommercial banana cultivars

Banana cultivars––Luvhele (MusaABB), Mabonde (MusaAAA), and Muomva-red (Musa balbisiana) ––were characterized for morphological, physicochemical, and antioxidant properties. All three cultivars varied significantly (P < 0.05) in their morphology, pH, titratable acidity and total soluble solids with no significant difference in their ash content. Individual cultivars showed variations in flour starch granule when observed using a scanning electron microscope. Characterization of cultivars for total polyphenols (TPs) and antioxidant activity upon pretreatment with ascorbic, citric, and lactic acid shows that the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay of samples varied significantly as Muomva-red cultivar (1.02 ± 0.01 mg GA/g) expressed the highest DPPH activity at lactic acid concentration of 20 g/L. Total polyphenol content was also highest for Muomva-red [1091.76 ± 122.81 mg GAE/100 g (d.w.)]. The high amount of TPs present in these cultivars make them suitable source of bio-nutrients with great medicinal and health functions.

Phenolics and essential mineral profile of organic acid pretreated unripe banana flour

Banana fruit (Musa spp) though rich in essential minerals, has also been implicated for the presence of phytochemicals which nonetheless beneficial, can also act as mineral inhibitors when in forms such as phenolic compounds, phytates and tannins. This study assayed the essential macro and trace minerals as well as phenolic compounds present in unripe banana flour (UBF) obtained from the pulp of four different cultivars. Unripe banana flour was processed by oven drying in a forced air oven dryer at 70°C upon pretreatment with ascorbic, citric and lactic acid. Organic acid pretreatment was done separately on each unripe banana cultivar at concentrations of 10, 15 and 20g/L. Phenolic compounds were profiled using liquid chromatography mass spectrometry electrospray ion (LC-MS-ESI) while essential minerals were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and mass spectroscopy (ICP-MS) respectively. Results of LC-MS-ESI assay of phenolics revealed the presence of flavonoids: epicatechin and myricetin 3-O-rhamnosyl-glucoside in varying concentrations in UBF. Essential mineral profile indicated that Zinc had the least occurrence of 3.55mg/kg (p<0.05), while potassium was the most abundant mineral at 14746.73mg/kg in UBF of all four banana cultivars. Correlation between phenolic compounds and essential minerals using Pearsons Correlation Coefficient test revealed weak and inverse association between flavonoids and most macro and trace minerals present in UBF samples. Organic acid pretreatment thus exhibited little effect on phenolics and essential minerals of UBF samples, though, inhibitory influence of phenolic compounds was recorded on essential minerals.