THE DEVELOPMENT OF JUVENILES OF HETERODERA-SCHACHTII IN ROOTS OF RESISTANT AND SUSCEPTIBLE GENOTYPES OF SINAPIS-ALBA, BRASSICA-NAPUS, RAPHANUS-SATIVUS AND HYBRIDS

The development of Heterodera schachtii Schm. (beet cyst nematode, BCN ) juveniles in roots of resistant and susceptible genotypes belonging to cruciferous crop species and hybrids was studied from 4 to 28 days after inoculation. No difference in root penetration by larvae was obs erved between resistant and susceptible plants. The development of nem atodes in roots from resistant plants of Raphanus sativus L., resistan t X Brassicoraphanus Sageret and a resistant hybrid X Brassicoraphanus X Brassica napus L. was similar. BCN resistance in these three source s of plant material appeared to be related to an increased male:female nematode ratio as compared to the ratio found in susceptible R. sativ us plants. Also in resistant plants of Sinapis alba L. and a resistant intergeneric hybrid S. alba x B. napus the increase in male:female ne matode ratio, as compared to the ratio found for susceptible S. alba c ultivars and a susceptible intergeneric hybrid S. alba X B. napus, see med to be related with the observed resistance. In roots of the resist ant S. alba and of a resistant hybrid S. alba X B. napus, however, BCN resistance might also be due to a slower development of larvae and in creased necrosis of root cells at the site of larval penetration.