S. Matthews

Seed vigour in cultivars of dwarf French bean ( Phaseolus vulgaris ) in relation to the colour of the testa

Differences in the field emergence of 30 commercial seed lots of dwarf French beans were associated with the colour of the testa, the 11 lots with a white testa having a lower mean field emergence of 67% compared with 91% for lots with black (11 lots) or brown (8 lots) testae. The white-seeded lots also had higher leachate conductivities (mean 42 μ S/cm/g) and imbibed more rapidly (an average 43% weight increase after 6 h imbibition) than black- or brown-seeded lots (average 25 μS/cm/g; 30% weight increase). The extent of damage to the testa which was slight in all lots was not related to differences in either the field emergence or rate of imbibition of the lots. In two successive imbibition cycles seeds of Provider (brown testae) took up water far more rapidly in the second imbibition (78% weight increase after 3 h) than the first (25% weight increase). The coloured testae normally adhere very tightly to the cotyledons but were loosened following the first imbibition leading to a more rapid uptake of water. The rapid imbibition of Tenderette (white testae) which has a loose fitting testa even in the dry seed was increased only slightly by a second imbibition. When seeds were imbibed from one end only from which the testa was removed Tenderette imbibed rapidly (90% weight increase after 12 h) whereas in Provider the tightly adhering testa limited the rate of water uptake (42% weight increase after 12 h) despite the ready access of water to the seed. It is suggested that the degree of adherence of the testa to the cotyledons is the major factor influencing the rate of imbibition of cultivars of dwarf French beans differing in testa colour and its role in determining seed vigour is discussed.

Seedling vigour and susceptibility to diseases and pests

The emergence and early seedling growth of pea, faba bean (field and broad bean), chickpea and lentil can be reduced by both seed- and soil-borne fungi. The susceptibility to soil fungi in pea is largely due to areas of dead tissue on the cotyledons, caused by both ageing and rapid imbibition, resulting in the leakage of solutes into soil. The influence of dead tissue and leakage on fungal growth is discussed, as is the evidence for similar phenomena in the other crops. The significance of seedling vigour in relation to pests is considered and exemplified by the effects of leaf weevil (Sitona lineatus) on pea and faba bean.