6.33
SOME PECULIARITIES OF DEVELOPMENT OF TWO BOTRYTIS SPECIES ON ALLIUM CEPA BULBS

AK KHRAMTSOV1, NP KOOPREYENKO2, AA MELESHKEVICH2 and AS SHUKANOV1

1Department of Botany, Belarus State University, Skoriny Str. 4, Minsk, Belarus; 2Byelorussian Vegetables Research Institute, Mayakovskij Str. 127, Bldg 1, Minsk, Belarus

Background and objectives
Onion is one of the most important vegetable crops. However, in some years losses of bulbs exceed 50% at harvest [1]. The main cause of losses is phytopathogenic microorganisms, among which a considerable role is played by Botrytis. The aim of this research work was to study the peculiarities of the development of the fungi Botrytis cinerea and B. allii in the tissues of second-year bulbs of Allium cepa in storage.

Materials and methods
The materials used were second-year bulbs of pungent variety Vetraz (V) (white coloration of succulent scales) and half-pungent variety Krivitsky Roozhovye (KR) (pink coloration of succulent scales), and isolates of B. cinerea and B. allii. The inoculation of negatively selected healthy bulbs was made by water-suspension of conidia (1.5-2x106/ml) of the pathogens studied. The inoculation of mechanically damaged and undamaged bulbs was made by every pathogen separately. lnoculum (0.1 ml) was spread over the whole surface in the case of damaged plants, and with undamaged ones it was placed on a dry scale in the lateral part of a bulb. The degree of bulb damage caused by disease was registered every 1Oth day according to the nine points of the scale [2]. The indices of temperature and relative humidity of the air in the store were l0C and 70%, respectively.

Results and conclusions
The first symptoms of the disease on both varieties under study became apparent on the 11th day from the moment of inoculation in the case of both B. allii and B. cinerea. The rot, caused by both pathogens tested, does not penetrate deep into the tissues of a bulb, but spreads unevenly and it is developed under dry scales, mainly in a meridional direction. The distinctive feature of pathogenesis of bulbs of variety KR is decoloration of damaged parts of the tissue. The duration of fungal development differs considerably, being 46 days for B. allii (both varieties), 67 days for B. cinerea (variety KR) and 77 days (variety V). This effect is not only connected with ecological factors (temperature, relative humidity of the air), but also with the differences in susceptibility of two varieties to pathogens studied. The development of rot in the traumatized bulbs of the varieties under study differs depending on the pathogen. In the case of infection by B. allii, three times as much rot develops as with B. cinerea (variety V). When affected by B. allii, the development of rot on the bulbs of variety KR is twice as much as that caused by B. cinerea. The results obtained may be explained by the fact that B. allii is a strictly specialized pathogen of onion and B. cinerea is a typical polyphage. The development of disease caused by B. allii is greater in the beginning with variety V, but starting already with the 8th registration and further on, the development of the disease was much lower on the plants of this variety than on the compared ones. The development of the disease caused by B. cinerea increased faster than on bulbs of the variety KR.

These findings do not prove the suggestion of a favourable influence of anthocyanes on the preservation of onions. For the period of this research no symptoms of rot were observed in the plants inoculated without any mechanical damage; undamaged dry scales served as a reliable protection of bulbs of the tested varieties from infection by the spores B. allii and B. cinerea under storage.

References
1. Koopreyenko NP, 1996. Abstracts of a Scientific Conference on the Problems of Phytopathology in the Republic of Belarus, p. 30.
2. Anon., 1980. The Wide Unified Classifier of COMECON and International Classifier of COMECON of Onion (Allium cepa L.). Olomoyts.