Mean germination day and speed germination of onion seeds

Abstract

Two experiments were carried out at the Seed Testing Laboratory of Unidade Executiva de Pesquisa Agropecuária (UEPAE-Pelotas, RS) of Empresa Brasileira de Pesquisa Agropecuária (EMBRARA) in February and May 1976. Four onion seed lots of the cultivar Baia periforme, with different germination percentages (64%, 74%, 80% and 90%) were used in the tests (BIANCHETTI 1976). A uniform length of 2 cm was established for seedlings removed daily for evaluation of plant development (normal or abnormal). The use of a new experimental design, the latin cube (AMARAL & BIANCHETTI 1977) allowed local control in the three directions within the germinator. The experimental results indicated that positioning of the germination boxes inside the germination had no influence over the percentage, but it affected other parameters studied. The THRONEBERRY & SMITH (1955) index of germination speed (WOODSTOCK 1973) was determined for all four seed lots. The value of this index as a characteristic of vigor was discussed. Its main limitation lies in that it estimates the germination speed for the lot, including viable and non-viable seeds. Since this estimation is influenced by the germination percentage, this index underestimates the germination speed. This underestimation grows larger as the germination percentage becomes lower. A new index - the germination speed of viable seeds - proposed by AMARAL (1973) was used to eliminate this underestimation. The variances were not homogeneous for the THRONEBERRY & SMITH (1955) index, but were so for the index of germination speed of viable seeds. A negative correlation was found between the germination speed of viable seeds and the germination percentage, possibly accounted for by a greater influence of weathering on the later seeds of the sample. The index of germination speed, proposed by Amaral, accompanied by the germination percentage, is much more informative than the one proposed by THRONEBERRY & SMITH (1955). The comparison of the coefficients of variation indicated that the index of germination speed of viable seeds was more precise than the mean germination day. Through the comparison of F values, it was found that the index of germination speed of viable seeds was more  than the mean germination day to the effects of the treatment (lots) and of the location inside the germinator. Thus, the average lenght of the germination period estimated through the germination speed of viable seeds, should be preferred to the mean germination day calculated by the usual formula.