“…However it is difficult to provide a satisfactory infection pressure in the field and repeatable testing conditions (Lapwood, 1965;Ullrich, 1967;Sch6ber, I987;Dorrance & Inglis, 1998;Platt & Tai, 1998). However it is difficult to provide a satisfactory infection pressure in the field and repeatable testing conditions (Lapwood, 1965;Ullrich, 1967;Sch6ber, I987;Dorrance & Inglis, 1998;Platt & Tai, 1998).…”