4. Discussion
4.1. Survival of plantlets 8 weeks after deflasking
The survival of plantlets was dependent on type of product and
was influenced by soil types. In the non-inoculated soils, survival
of inoculated plants was not significantly different for most products
except for PHC Colonize that negatively affected survival (less
than 50.0% survival rate). The study showed hardening with soils
combined with products to be more effective than using the conventional
media. An increase in plant survival of over 33.0% was
realized with Bacillus (Subtilex and PHC Biopak) inoculation in
the Vertisol and mycorrhizae and Bacillus in the Rhodic Ferralsol
compared to the non-inoculated plants in the conventional media.
In the Vertisol and Humic Nitisol, the survival of non-inoculated
plantlets consistently superseded that in the conventional media
indicating use of non-amended soils as a better, more profitable
option for hardening. This is however dependent on the composition
of microorganisms based product used for inoculation and
the prevailing soil chemical, physical and nutritional conditions.
Mycorrhizal inoculation of plants, for example, in the conventional
media slightly enhanced survival of plants (7.0% and 13.0%
respectively by Rhizatech and MYCOR respectively). Plant growth
promoting bacteria (PGPB) as well as mycorrhizae have been
reported to enhance biomass production during the first stages of
crops and can contribute to plant adaptation from the in vitro to
the post vitro phase (Carletti, 2000). Jaizme-Vega et al. (2004) evaluated
the effect of a rhizobacteria consortium of Bacillus spp. on
the first developmental stages of two micropropagated bananas
and concluded that this bacterial consortium can be described as
a prospective way to increase plant health and survival rates in
commercial nurseries. Table 7
While the mycorrhizal products and the multiple species Bacillus
product (PHC Biopak) efficacy on survival was restricted to
specific soils, the single species Bacillus product (Subtilex) was different
in supporting survival of plants in both the Rhodic Ferralsol
and Vertisol. This study therefore reveals a differential performance
of single and multiple species mycorrhizal and Bacillus
products. Positive effects of single and multiple plant growth promoting
bacteria (PGPB) and arbuscular mycorrhizal fungi (AM
fungi) species have been reported separately. A Bacillus consortium
containing strains INR7, T4 and IN 937b strains inoculation
to different tissue culture (TC) banana cultivars under normal
nursery conditions consisting of soil:volcanic ash:peat substrate
mixture was reported to improve survival and growth (Rodriguez-
Romero et al., 2005). Differential functioning of AM fungi species
on banana growth has also been reported., Glomus etunicatum
enhanced growth and nutrient uptake better than the indigenous
isolate for plants established in an Andisol mixed with a fungicide
and inorganic fertilizer while the indigenous isolates was more
effective in sterile sand medium (Juma, 2011).