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Sphaerotheca fuliginea on cucurbits in Saudi Arabia
506
Notes and brief articles
SPHAEROTHECA FULIGINEA ON CUCURBITS IN SAUDI ARABIA ZAYDAN M. ABUL-HAYJA AND IBRAHIM Y. TRABULSI
Department of Crop Protection, College of Agriculture, Riyad University, Riyad, Saudi Arabia
Powdery mildew of cucurbits is a serious disease in the central region of Saudi Arabia. It occurs on squash (Cucurbita pepo L.), melon (Cucumis melo L.), watermelon (Citrullus vulgaris Schrad.), and cucumber (Cucumis sativus L.). Both Erysiphe cichoracearum DC. ex Merat. emend. Salmon and Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll. have been implicated as causal agents of the disease. Since the two pathogens are similar in their conidial stages, it is difficult to distinguish between them in the absence of the sexual stage. Zaracovitis (1965) showed that conidia of S. fuliginea formed characteristic forked germ tubes whereas those of E. cichoracearum produced appressoria upon germination. He concluded that Oidium spp. from cucumber and marrow were imperfect stages of S. fuliginea and not E. cichoracearum as was claimed by Stone (1962). Our attempts to identify the pathogen on cucumber in Saudi Arabia were inconclusive. Based on conidia and germ tube characters, identification as E. cichoracearum was favoured since neither fibrosin bodies nor forked germ tubes were observed. Abundant cleistothecia were discovered fortuitously on squash cv. Cocozella and White Bush in the College of Agriculture farm, Riyad, where the mildew was maintained around the year for disease resistance work, and on cucumber at Khar], 80 km south of Riyad, Saudi Arabia.
Trans. Br. mycol. Soc. 76 (3), (1981).
The mycelium was abundant and spreading on upper and lower surfaces of leaves, and in patches on stems and petioles. Conidia were ellipsoid to doliiform, measuring 27'2-39'8 x 14'4-19'8 pm and borne in long chains. Cleistothecia were gregarious, more or less spherical, orange-brown, and measured 66-108 pm. Appendages were brown, mycelioid, interwoven with mycelium and variable in shape and size. Numbers of appendages per cleistothecium ranged between three and thirteen and their length between 63 and 270 pm. The ascus was broadly ellipsoid to spherical, measuring 42-75 x 30-63 pm. Ascospores were four to eight and ellipsoid to nearly spherical (Fig, 1). No significant differences were noted between the pathogen on squash and cucumber. Based on the cleistothecia observed, the causal agent for powdery mildew on squash and cucumber and probably all cucurbits in Saudi Arabia is Sphaerotheca fuliginea and not Erysiphe cichoracearum.
REFERENCES
STONE, O. M. (1962), Alternate hosts of cucumber powdery mildew. Annals of Applied Biology 50, 203-210. ZARACOVITIS, C. (1965). Attempts to identify powdery mildew fungi by conidial characters. Transactions of the British Mycological Society 48, 553-558.
Printed in Great Britain
°007-1536/81/2828-7520 $00.35 © 1981 The British Mycological Society
Notes and briefarticles
SO 11 m
/
A
B SOllm
c Fig.
1.
Cleistothecia of Sphaerotheca fuliginea. (A) On cucumber; (B) on squash: note ellipsoidal ascus and ascospores; (C) on squash: note spherical ascus and dark myceloid appendages.
Trans. Br. mycol, Soc. 76 (3), (1981).
Printed in Great Britain
0007-1536/81/2828-7520 $00.35 © 1981 The British Mycological Society
5°7
Notes and brief articles
SPHAEROTHECA FULIGINEA ON CUCURBITS IN SAUDI ARABIA ZAYDAN M. ABUL-HAYJA AND IBRAHIM Y. TRABULSI
Department of Crop Protection, College of Agriculture, Riyad University, Riyad, Saudi Arabia
Powdery mildew of cucurbits is a serious disease in the central region of Saudi Arabia. It occurs on squash (Cucurbita pepo L.), melon (Cucumis melo L.), watermelon (Citrullus vulgaris Schrad.), and cucumber (Cucumis sativus L.). Both Erysiphe cichoracearum DC. ex Merat. emend. Salmon and Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll. have been implicated as causal agents of the disease. Since the two pathogens are similar in their conidial stages, it is difficult to distinguish between them in the absence of the sexual stage. Zaracovitis (1965) showed that conidia of S. fuliginea formed characteristic forked germ tubes whereas those of E. cichoracearum produced appressoria upon germination. He concluded that Oidium spp. from cucumber and marrow were imperfect stages of S. fuliginea and not E. cichoracearum as was claimed by Stone (1962). Our attempts to identify the pathogen on cucumber in Saudi Arabia were inconclusive. Based on conidia and germ tube characters, identification as E. cichoracearum was favoured since neither fibrosin bodies nor forked germ tubes were observed. Abundant cleistothecia were discovered fortuitously on squash cv. Cocozella and White Bush in the College of Agriculture farm, Riyad, where the mildew was maintained around the year for disease resistance work, and on cucumber at Khar], 80 km south of Riyad, Saudi Arabia.
Trans. Br. mycol. Soc. 76 (3), (1981).
The mycelium was abundant and spreading on upper and lower surfaces of leaves, and in patches on stems and petioles. Conidia were ellipsoid to doliiform, measuring 27'2-39'8 x 14'4-19'8 pm and borne in long chains. Cleistothecia were gregarious, more or less spherical, orange-brown, and measured 66-108 pm. Appendages were brown, mycelioid, interwoven with mycelium and variable in shape and size. Numbers of appendages per cleistothecium ranged between three and thirteen and their length between 63 and 270 pm. The ascus was broadly ellipsoid to spherical, measuring 42-75 x 30-63 pm. Ascospores were four to eight and ellipsoid to nearly spherical (Fig, 1). No significant differences were noted between the pathogen on squash and cucumber. Based on the cleistothecia observed, the causal agent for powdery mildew on squash and cucumber and probably all cucurbits in Saudi Arabia is Sphaerotheca fuliginea and not Erysiphe cichoracearum.
REFERENCES
STONE, O. M. (1962), Alternate hosts of cucumber powdery mildew. Annals of Applied Biology 50, 203-210. ZARACOVITIS, C. (1965). Attempts to identify powdery mildew fungi by conidial characters. Transactions of the British Mycological Society 48, 553-558.
Printed in Great Britain
°007-1536/81/2828-7520 $00.35 © 1981 The British Mycological Society
Notes and briefarticles
SO 11 m
/
A
B SOllm
c Fig.
1.
Cleistothecia of Sphaerotheca fuliginea. (A) On cucumber; (B) on squash: note ellipsoidal ascus and ascospores; (C) on squash: note spherical ascus and dark myceloid appendages.
Trans. Br. mycol, Soc. 76 (3), (1981).
Printed in Great Britain
0007-1536/81/2828-7520 $00.35 © 1981 The British Mycological Society
5°7