Mycelium on potato-dextrose agar, chalk white. Pycnidia appearing within 1-2 weeks in air-conditioned laboratory (20-25 C), black, flask shaped, bluntly conical (250-1000 µm). Spores exuding through ostiole in whitish to deep yellow tendrils. Two types of spores present; conidia and stylospores. Conidia hyaline, unicellular, ovate, 6.9 x 2.4 µm, usually biguttulate. Stylospores hyaline, filiform, curved at one end, averaging 20.5 x 1.6 µm, not observed to germinate. Older cultures tan to light brown. Colony margins and scattered zones black at surface and deep in agar. Perithecia (several to 50, or more) embedded in usually distinct, black, elevated stroma (Figs. 1, 2) erumpent singly or in irregular clusters, black, globose, commonly 150-460 µm in diam, ostiolate, with necks sinuous, filiform, 470-900 x 50-120 µm. Tip of neck bluntly rounded, brown. Asci clavate, sessile, 29-40 x 5.2-7.3 µm (Fig. 3). Ascospores biseriate, hyaline, 2-celled, constricted at the septum, fusoid to ellipsoid, 8.9-9.4 x 3.1 µm, exuding in white to cream colored drops of liquid, often accompanied by stylospores.

Perithecia per bimenstruum in agaro cum solani tuberibus et dextroso composito culta in stromate immersa, singula vel in gregibus irregularibus emergentia, nigra, globosa, vulgo 150-460 µm diametro, ostiolata, collis sinuosis, filiformibus, 470-900 x 50-120 µm. Summum collum obtuse rotundatum, brunneum. Asci clavati, sessiles, 29-40 x 5.2-7.3 µm. Ascosporae biseriatae, hyalinae, bicellulares; ad septum constrictae, fusoideae vel ellipsoideae, 8.9-9.4 x 3.1 µm, cellula utraque vulgo biguttulata. Pycnidia lagunculiformia, nigra, in mycelio albo inplicato per dies duodecem adolescente evoluta, 250-1000 µm diametro, obtuse conica, plerumque multilocularia. Conidia hyalina, ovata, unicellularia, 6.9 x2.4 µm, plerumque biguttulata. Stylosporae 20.5 x 1.6 µm. hyalinae, continuae, filiformes, fine uno curvata. Habitat in fructibus Actinidiae chinensis.

Diaporthe actinidiae resembles D. medusaea Nit. as described by Wehmeyer (2) but differs most obviously in the smaller asci and ascospores.
Hyphal tips from germinating single ascospores produced pycnidia with conidia and stylospores. After 6-8 weeks in an air-conditioned laboratory (20-25 C), perithecia were produced in some, but not all, single-ascospore cultures on PDA in Petri dishes or culture tubes.
The optimum temperature for mycelial extension on potato-dextrose-yeast-extract (0.5%) agar (PDY) was near 20 C (FIG. 4). The maximum temperature for extension was about 35 C. Detectable growth occurred at 0 C within 9 da suggesting that the absolute minimum temperature for growth might be several degrees below 0 C. Germination of conidia was near 100% within 24 hr on PDY at 20, 25, and 30 C (FIG. 5) but was absent at 5 or 40 C. The optimum temperature for germ tube elongation was near 25 C.
Pathogenic growth was tested by wound inoculations of surface sterilized Chinese gooseberry fruits of the Hayward cultivar. A dissecting needle was used to wound the fruits 10 or more times to a depth of 2-3 mm at the stem end. After immersion in a spore suspension (6 x 10⁶ conidia/ml), fruits were placed in perforated polyethylene bags at constant temperatures. Disease symptoms were visible after 3 da at 25 and 30 C with slightly larger lesions at 30 C. to 35 C, a temperature that injured the fruit, disease development was slight. No disease symptoms were observed after 9 da at 15 C nor after 30 da at 0 C.

The type specimen has been deposited in the National Fungus Collections (BPI 71849), Beltsville, Maryland, and cultures have been provided the American Type Culture Collection, Rockville, Maryland (ATCC 28096).