First report of banana freckle disease caused by Phyllosticta cavendishii in Mauritius

Banana (Musa sp.) is among the most important fruit crops grown in Mauritius with significant socioeconomic and cultural considerations. The annual production of banana approximates to around 8000 tonnes (Statistics Mauritius, 2018). Dwarf Cavendish main variety commercially Mauritius. During hot humid month February 2014, symptoms consisting dark black spots were observed on unripe from region Nouvelle Découverte (super zone). A disease incidence more than 50% a moderate severe level severity across field was reported by extension services Food Agricultural Research Extension Institute. On fruits, initial symptom tiny reddish-brown spots, bordered green water-soaked margins (Figure 1). As enlarged coalesced, surface became rough turned black. These had texture like sand-paper, similar description described Wong et al. (2012). Comparable leaves 2). Results rapid island-wide survey showed that only Cavendish-type varieties displayed infection. Out 98 fields surveyed (50.9 ha), 65% affected. Morphological identification suspected fungal pathogen done using compound light microscope. sterile needle used tease pycnidia drop water release conidia, before being mounted clear lactic acid for microscopic examination. Conidia 3) formed singly at apex conidiogenous cell hyaline, aseptate, oblong ellipsoidal, coarsely guttulate measured 7.1-15.6 × 4.4-8.3 μm. apical mucilaginous appendage arising conidium straight curved 5.1-12.9 μm long. Spermagonia 70–125 diameter 50–85 high. Dumbbell-shaped spermatia 4) biguttulate 7.5-9.5 1.3-1.8 morphological characters are consistent species Phyllosticta cavendishii (Wong al., 2012). Lesions 11 samples leaf fruiting bodies ground liquid nitrogen followed genomic DNA extraction. Extraction c. 50 mg fresh plant tissue Biosprint 15 Plant Kit (Qiagen, Germany). Tissues first homogenized Tissuelyser Germany) 2 ml microcentrifuge tube containing 3 mm metal bead two 30 second bursts 30Hz. Two microliters eluted as template an ITS PCR amplification AmpliTaq Gold 360 Mastermix (Applied Biosystems, USA) 0.5 μM each primers GMF1 GMR2 Thermal cycling conditions 95°C 10 min 40 cycles sec, 55°C sec 72°C 1 min. Final products Amplicons (550bp) directly sequenced same primer pair. Resulting sequences analysed BlastN well manual comparison known isolates which cause freckle banana. causal agent all tested found be cavendishii. deposited GenBank (Accession Nos. MW520341-MW520351) Queensland Pathology Herbarium (BRIP 72048 72058). Pathogenicity twenty mature healthy fruits Cavendish. Fruits sterilised 0.2% sodium hypochlorite mins, rinsed distilled allowed dry inoculation. Ten artificially inoculated outer surface, clearly marked, conidial suspension 106 conidia/ml, prepared extracted infected tissue. Control treated water. All covered plastic bags 48 hours incubated room temperature, 80% relative humidity 12-hour photoperiod. After 7 days, typical minute identical those field, appeared whereas controls remained healthy. characteristics fungus previously observed, hence fulfilling Koch's postulates. To our knowledge, this report causing authors acknowledge Centre Science, Alliance Agriculture Innovation molecular also Dr Yu Pei Tan Brisbane accessioning submission into GenBank.