Effects on saffron growth
The overall pattern of growth responses to the group of 5 treatments was successfully and
precisely replicated in two seasons of growth for all of the experimental treatments (Table 1).
Differences were observed, however, between treatment groups. Compared to the controls,
application of B. subtilis to saffron corms significantly increased leaf length, flowers per corm,
weight of the first flower stigma, and total stigma biomass; it also significantly decreased the
time required for corms to sprout. In contrast, the number of shoot sprouts significantly
decreased beyond that of the untreated controls (Table 1). The beneficial effects of B. subtilis
on saffron corm growth also differed depending on how the corms were treated with the
microbe. For example, although the microbe stimulated faster shoot emergence from the soil,
this only occurred under the T2 conditions, where corms were soaked in the B. subtilis spore
solution 15 min before sowing. The T2 treatment also significantly maximized leaf length, the
number of flowers produced by each corm, and stigma biomass in the first flower beyond that
of the controls (Table 1). Similar stimulation of shoot growth was observed by others when B.
subtilis was applied to tomatoes (Lycopersicon esculentum Mill.) [22]. Although there were
longer shoots produced, the number of shoots sprouting per corm was not increased by any of
the bacillus treatments. The mechanism of growth stimulation by plant growth–promoting
rhizobacteria is unknown, however, Bacillus species do produce plant growth hormones,
namely gibberellic acid and an auxin, indole-3-acetic acid (IAA) [13], [14], [21]. It is possible,
therefore, that these compounds may be the agents stimulating the observed saffron growth