INDEX WORDSBrassica spp ., shatter-resistance, siliqua strength, field shatter . SUMMARY A new test procedure for measuring shatter-resistance of siliquae of Brassica s pp . i s described . A siliqua with its proximal end clamped is loaded as a cantilever in a testing machine . The maximum bending moment, the corresponding stiffness and the energy to cause the siliqua to rupture were taken as measures of the resistance of the siliqua to shatter . Studies showed that ranking of accessions based on either bending moment or energy closely approximated the rankings based on observations of field shatter . A reasonably high significant negative correlation was found between percentage of shattered siliquae and both bending moment and energy (r = -0 .595 and -0 .531 respecitvely, P = 0 .001). The above results indicated that bending moment and energy could be used as criteria in evaluating rapeseed genotypes for shatter-resistance in breeding programmes .

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A small impact pendulum was developed to measure the shatter resistance of seed pods. While clamped by their stems, the pods are hit by the rigid pendulum; the rupture energy is derived from the measured angles of swing. The consistency of the pendulum was confirmed by tests on a sample of fine spring wire. The pendulum was then used in a series of trials on 13 rapeseed varieties and rupture energy results were compared with earlier bending moment and bending energy results obtained from tests using a quasi‐static cantilever arrangement. Rupture energy values were much less variable than bending energy. However, the ranking of varieties by all three strength measures was generally similar.

KADKOL, G. P., G. M. HALLORAN, and R. H. MACMILLAN. 1986. Inheritance of siliqua strength in Brassica campestris L. I.Studies of F2 and backcross populations. Can. J. Genet. Cytol. 28: 365-373. The inheritance of siliqua strength was studied in Brassica campestris L. using F1, F2, and backcross generations of crosses between cv. Torch (shatter susceptible) and var. Yellow Sarson and var. Brown Sarson (shatter resistant) accessions. Shatter resistance (high siliqua strength) was recessive in all crosses. Crosses involving DS-17-D (var. Brown Sarson) indicated that siliqua strength is most likely controlled by two genes that show dominant epistatic interaction. Crosses of IB-5 and B-46 (both var. Yellow Sarson) each with cv. Torch indicated the likelihood of three genes controlling siliqua strength, two of which appeared to be epistatic over the third gene when dominant. In these crosses, the multivalve character appeared to be controlled by three genes, two of which were epistatic over the third gene resulting in multivalve character when the former two were recessive. Segregation for siliqua strength in the var. Yellow Sarson crosses was not independent of segregation for multivalve character.Key words: Brassica, siliqua strength, shatter resistance, Sarson. KADKOL, G. P., G. M. HALLORAN et R. H. MACMILLAN. 1986. Inheritance of siliqua strength in Brassica campestris L. I. Studies of F2 and backcross populations. Can. J. Genet. Cytol. 28: 365-373. La transmission hkrkditaire de la fermetk des siliques a kt6 ktudike chez Brassica campestris L., en utilisant les gknkrations F1 et F2, et celles de rktrocroisements, obtenues des croisements entre le cv. Torch, susceptible aux bris, et les obtentions jaunes et brunes de Sarson, rksistantes aux bris. La rksistance aux bris, ou fermetk Clevke des siliques, fut rkcessive chez tous les croisements. Les croisements impliquant le Sarson brun DS-17-D ont indiquk que la fermetk des siliques ktait tres probablement contrblke par deux genes qui ont une interaction kpistasique dominante. Les croisements impliquant deux Sahsons jaunes, IB-5 et B-46, chacun avec le cv.Torch, ont indiquk la possibilitk que trois genes contrblent la fermetk des siliques, dont deux apparaissent kpistasiques au troisieme, lorsqu'ils sont dominants. Dans ces croisements, le caractere plurivalvulk semble etre contrblk pah trois genes, dont deux sont kpistasiques au troisieme, ce qui conduit h l'expression plurivalvulk lorsque les deux premiers sont rkcessifs. La skgrkgation pour la fermetk de la silique chez les croisements de Sarsons jaunes ne s'est pas avkrke indkpendante de la skgrkgation pour le caractere plurivalvulk.

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