Ascochytula, Ascochytella, Ascochyta and related fungi, with special reference to Ascochyta paspali

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ABSTRACT

Two Coelomycete genera, Ascochytula Died. and A s c o c h y t e l l a Tassi, were s t u d i e d i n o r d e r t o determine t h e i r g e n e r i c a f f i n i t i e s , e s p e c i a l l y w i t h Ascochyta. Ascochytula obiones (Jaap) Died.

,

t h e t y p e species o f Ascochytula, i s considered t o be congeneric w i t h Ascochyta p i s i L i b . ,

~

t h e t y p e species o f t h e e a r l i e r genus, Ascochyta L i b . Ascochytula i s thus

~

reduced t o synonymy w i t h Ascochyta. O f t h e t h i r t y - s i x species and two v a r i e t i e s named i n , o r d i r e c t l y associated w i t h , Ascochytula, twenty a r e h e r e i n described as species o f Ascochyta and f o u r a r e excluded from

Ascochyta. The remaining species were e i t h e r n o t examined, o r a r e nomina dubia. The f o l 1 owing names are proposed : Ascochyta asparagina ( P e t r a k ) comb. nov., - A. deformis (P. Karsten) comb. nov.

, -

A. d o r y c n i i ( P e t r a k ) comb.

nov., - A. l u d w i g i a n a ( P e t r a k ) comb. nov., - A . moravica (Petrak) comb. nov., A. obiones (Jaap) comb. nov., A. p h l o m i d i c o l a nom. nov., and A. u l i c i s (Grove)

- - -

I

comb. nov.

A s c o c h y t e l l a Tassi, which has o f t e n been confused w i t h Ascochytula, i s a l s o synonymised w i t h Ascochyta. The o r i g i n a l t h i r t e e n species i n

A s c o c h y t e l l a were examined, and - A. v i c i n a (Sacc.) Tassi chosen as t h e l e c t o -

I type species. Most o f t h e t h i r t e e n species a r e regarded as being e i t h e r 1 misplaced i.n Ascochytella, o r nomina dubia, and o n l y f o u r , i n c l u d i n g t h e l e c t o t y p e , a r e accepted as species o f Ascochyta. The name, P l a c o d i p l o d i a c a n t h i i f o l i a (Cooke & Massee) comb. nov. i s proposed.

The t y p e species of Ascochyta, and o f s i x r e l a t e d genera, Ascochytulina Petrak, Coniothyrium Corda, D i p l o d i n a Westend., Pseudodiplodia (P. Karsten) Sacc., Scol e c o s p o r i e l l a P e t r a k, and Stagonospora (Sacc. ) Sacc. were s t u d i e d t o detemi.ne t h e d i s t i n c t i o n s between these s i x genera and Ascochyta.

M i c r o d i p l o d i a A l l e s c h e r and D i p l o d i a Fr. a r e a l s o discussed, i n r e l a t i o n t o Ascochvta.

Ascochyta paspal

i

(H. Sydow) Puni th.

( s

Ascochytul a paspal i H. Sydow) ,

which causes a leaf stripe disease of Paspalum dilatatum Poir., an

important perennial grass of northern North Is1 and pastures, was examined in detail. At some temperatures, under controlled climate conditions, the fungus significantly reduced the yield of

-

P. dilatatum. - A. paspal

i

was

I

found to grow systemically, as mycelium within the xylem vessels, and was able to infeci all parts of the plant, including the roots and seeds.

Green leaves sometimes became infected systemically without production of visual symptoms. Infected seed is suggested as a means for disease spread.

No

teleomorph for -

A .

paspali was found, and the fungus is thought to over- winter in the dormant grass. The seasonal fluctuation in levels of - P.

dilatatum and of the disease was studied in two Northland pastures with paspalum as a component. One pasture was studied for fourteen months, and the other for four months. Disease levels, and paspalum levels, were

determined by point quadrat analysis and by sorting of randomly cut samples.

Levels of both the host and of the disease peaked in summer, while both

were at low levels, or apparently absent, over the winter months.