Rhizosphere Microorganisms and Their Effect on Fruit Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 364

which correlated with the colonization of the root system and proliferation of the fungus
within the roots (Gianinazzi-Pearson et al., 2000; Liu et al., 2003). Regarding biochemical
and physiological changes found in mycorrhizal plants, it has been shown that specific
proteins (Gianinazzi-Pearson and Gianinazzi, 1989), amino acid fractions (Tawaraya et
al., 1994; Tawaraya and Saito, 1994), lipids (Bethlenfalvay et al., 1994, 1997), reducing
sugars, and secondary metabolites are produced by host plants in response to AMF root
colonization.
Interactions between PGPR and AMF have potentially beneficial functions, together
with the majority of those where PGPR (Meyer and Linderman, 1986; Kloepper, 1994,
1996) including nitrogen-fixing bacteria (Biro et al., 2000) are involved. There is little
information regarding the mechanisms controlling interactions of bacteria with AMF and
plant roots in the mycorrhizosphere; however, a number of possible alternatives have been
proposed. Some bacteria have been shown to directly affect AMF germination and growth
rate (Carpenter-Boggs et al., 1995); thus, the beneficial impact to the plant could be through
the mycorrhizal association.

17.4 Changes in product quality due to crop inoculation
with beneficial rhizosphere microorganisms

Appearance is utilized throughout the production chain as the primary means of judging
the quality of individual units of product. Product appearance is characterized mainly by
the absence of defects, size, shape, and color (Kays, 1999). The introduction of arbuscu-
lar mycorrhizal fungi and plant growth-promoting rhizobacteria for crop production not
only increases total yield, but also has a positive effect on appearance resulting in greater
marketable yields.

17.4.1 Marketable quality

Field and greenhouse experiments have shown increased yields and enhanced quality of
fruit and vegetables resulting from PGPR and AMF inoculation. By adapting such methods
of production, homogeneous produce quality is obtained at the time of harvest. Additionally,
we have observed that products belonging to the first harvest keep the best quality compared
to that obtained with conventional production methods.
Table 17.1 shows the results of a field experiment carried out in Jalisco, Mexico. Bell
pepper fruits produced through the conventional method were compared to those produced
by inoculating plants with commercial arbuscular mycorrhizal inoculants. Fruits were clas-
sified into four different quality categories following criteria of marketability (unpublished

Effect of the arbuscular mycorrhizal fungi bell pepper fruit quality

Table 17.1

Treatments First harvest Second harvest Third harvest

Conventional production R G R

Tec-Myc E E G

Endospore E G R

Commercial inoculants, Tec-Myc and endospore; E, excellent quality; G, good quality; R, regular
quality; L, low quality.