Powdery Mildew on Spinach (Spinacia oleracea L.)

Abstract

Symptoms resembling powdery mildew appeared on spinach crops during April and May in 2007. Infected plants have suppressed growth, smaller and degenerated young leaves. The affected leaves become yellowish and wilt in a short time. High temperatures and draught conditions cause drying out of the affected plants. The symptoms are similar to physiological degeneration but are found on single plants or on small groups of plants. When plants are carefully examined, fine, exogenic mycelium is found on the leave blades. The mycelium can be clearly seen close to the main veins where it becomes denser and forms mycelium patches. On the leaf and flower stalks and plant stems the mycelium is white and fine at the beginning, and later becomes grayish. Under microscope analysis ectophytic mycelia of exogenic origin and short chains of spores are observed. On short conidiophores, chains with two types of conidia are formed: macro conidia that are one-celled, colorless, thin-walled, elliptical to cylindrical, sized 24.5-28.4 x 17.5 μm; and micro conidia – ovoid to elliptical, sized 10.4-14.1 x 7.7 μm. Teleomorphs are found in groups or as a single structure mainly close to the leaf veins. They are roundish and have appendages with uncinate-circinate to helicoids apex, sized - 87.5- 150 μm. Cleistothecia have 4-5 to 8 asci (68.0 x 38.0 μm), with 4 to 8 elliptical ascospores, sized 15.5-22.0 х 11.0-17.5 μm. The causal agent of powdery mildew on spinach found in Bulgaria has been identified as Uncinula spp. (Sawadaea spp.), Euoidium type anamorph, subspecies spinaciae.

U oktobru i maju 2007. godine primećeni su simptomi na biljkama spanaća koji podsećaju na peplnicu. Inficirane biljke imaju slabiji porast, male i degenerisane mlade listove. Zahvaćeni listovi žute i za kratko vreme venu. Visoke temperature i suše dovode do sušenja obolelih biljaka. Simptomi su slični degenerativnim promenama fiziološkog porekla, ali se javljaju ili na pojedinačnim biljkama ili na manjim grupama biljaka. Prilikom pažljivog pregleda biljaka uočava se nežna, egzogena micelija na obodu lista. Micelija je jasno uočljiva u blizini glavnih lisnih nerava gde postaje gušća i formira spletove. Na lisnim i cvetnim drškama i stabljici micelija je u početku nežna i bela, a kasnije dobija sivkastu boju. Pod mikroskopom se uočava ektofitna micelija egzogenog porekla i spore u kratkim nizovima. Na kratkim konidioforama formiraju se nizovi dva tipa konidija: jednoćelijske, bezbojne, eliptične do cilindrične makrokonidije tankih zidova, veličine 24,5-28,4 x 17,5 μm; i mikrokonidije – jajaste do eliptične, veličine 10,4-14,1 x 7,7 μm. Teleomorfne strukture se pronalaze u grupama ili pojedinačno, uglavnom u blizini lisnih nerava. Okruglastog su oblika i imaju apendicese sa kukastim-prstenastim ili helikoidnim vrhom, veličine 87,5-150 μm. Kleistotecije imaju 4-5 do 8 askusa (68,0 x 38,0 μm) sa 4 do 8 elipsoidnih askospora, veličine 15,5-22,0 x 11,0-17,5 μm. Prouzrokovač pepelnice spanaća pronađen u Bugarskoj identifikovan je kao Uncinula spp. (Sawadaea spp.), bespolni stadijum tipa Euoidium, podvrsta spinaciae.