Amazonia brachiata Jacob Thomas & Hina Mohamed, 2021

Mohamed, Hina & Thomas, Jacob, 2021, A new species of Amazonia (black mildews) on Ixora brachiata from Western Ghats, India, Phytotaxa 523 (3), pp. 259-263 : 260

Amazonia brachiata Jacob Thomas & Hina Mohamed sp. nov. ( Figs 1 , 2 ) Mycobank No: 840242

Type:— India, Kerala, Vagamon Hills, 9°39’59.2”N 76°54’06.5”E, on leaves of Ixora brachiata Roxb. (Rubiaceae) , 27 September 2019, J. Thomas & H. Mohamed MTCHT! 441 (holotype) .

Epiphytic on the leaf surface of Ixora brachiata (Rubiaceae) . Colonies epiphyllous, subdense, hyphal branching opposite to alternate, acute to wide angles, loosely reticulate, cells 24–33 × 7–11µm (x = 28.3 × 14.4 µm, n = 10). Appressoria alternate, antrorse to substrorse, straight to curved, 31–41 µm (x = 35.3 µm) long, stalk cells cylindrical to cuneate, 11–18 µm (x = 14.8 µm) long, head cells lobed, entire to truncate 18–23 × 15–19 µm (x = 20.6 × 17.5 µm). Sexual morph: Perithecia scattered up to 138 µm (x = 87, n = 10) diameter. Ascospores, straight 4-septate, slightly constricted at septa, 39–43 × 19–20 µm (x = 41.8 × 20.5 µm, n = 10). Asexual morph: Phialides closely arranged, alternate to opposite, unilateral, mixed with appressoria and in separate mycelial branch, 17–26 × 7–10 µm (x = 22.6 × 8.7 µm, n = 10).

Etymology: — Named after specific epithet of the host plant.

Known distribution:— Vagamon Hills, Kerala, India.

Amazonia brachiata is compared to five other Amazonia spp. previously recorded from Rubiaceae ( Table 1 ). It is similar to A. polypoda Sydow (1917: 145) in terms of ascospore size, but has smaller perithecia (84–134 µm vs. 350–450 µm). The perithecia of A. brachiata and A. psychotriae are similar in size but the former has lobed, truncate, and long appressoria (31–41 µm vs. 15–18.5 µm), as well as larger ascospores (39–43 vs. 31–37.5 µm). Amazonia brachiata differs from all other species reported from Rubiaceae in that the phialides occur both in separate mycelial branches and mixed with appressoria, while in the other species the phialides are mixed with appressoria.

Figures

FIGURE 1. Amazonia brachiata. A, B. Living leaves infected with Amazonia brachiata. C. Microphotograph of colony. D. Pattern of mycelial branching. E. Mycelium with alternately arranged appressoria. F. Phialides. G. Mature perithecium. F. Germinating ascospore.

FIGURE 2. Amazonia brachiata.A. Mycelium with appressoria. B. Germinating ascospore. C. Phialides.