Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

366 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
The alleviation of water stress manifested by reaching acceptable fruit quality was
also reported by Mena-Violante et al. (2006). Under drought conditions, pepper plants
inoculated with any of the two AMF consortia–produced fruits with fresh weights (41.3 and
43.9 g) similar to those of fruits in noninoculated plants not subjected to drought (40.8 g).
Additionally, fruits from plants subjected to drought and inoculated with a consortium
reached the same size (width 5.0 cm; length 7.8 cm; pedicle length 4.6 cm) than those in
noninoculated plants not exposed to drought (width 4.8 cm; length 8.1 cm; pedicel length
4.4 cm). Thus, inoculation of plant with AMF consortia mitigated the detrimental effect of
water stress on fruit fresh weight and size.
Quality of tropical fruits is also improved through PGPR inoculation. Baset Mia et al.
(2005) demonstrated the positive effect of PGPR inoculation along with a reduction (67%)
of recommended N fertilizer on banana yield and quality. The authors suggested that strains
of Azospirillum brasilense and Bacillus sphaericus could be used for high yielding and
improved physical attributes such as finger weight, length, diameter, and pulp/peel ratio.
Moreover, we have performed field trials working together with local crop producers, where
the inoculation with AMF and PGPR have brought increases in marketable yields in pepper,
tomato, potato, strawberry, melon, and lettuce ranging from 15 to 35%, especially in the
very first three harvests (V. Olalde-Portugal, unpublished data).
17.4.2 Shelf life
Improving produce quality at harvest is associated with beneficial changes in the keeping
quality of the product during postharvest storage. It is desirable to achieve a longer shelf
life of horticultural products, minimizing quality-reducing alterations such as water loss,
drastic color changes, spoilage derived from pathogenic microorganism and softening,
among others. Our greenhouse experiments showed that the inoculation of tomato plants
with AMF enhanced tomato shelf life. The fruits of noninoculated plants decayed earlier
than those of inoculated plants. Seventy percent of fruits produced by AMF plants were still
marketable after 10 days of storage at 25 ◦ C, while only 33% of fruits from noninoculated
plants were not decayed at that time (Mena-Violante et al., 2003).
Regarding the practice of inoculation and introduction of more than one fungus and/or
bacterium into the target crops, we found that the AMF and PGPR inocula seem to have
a synergistic effect on tomato shelf life. Figure 17.1 shows the percentages of marketable
tomato fruits after 8, 15, 22, and 30 days of storage at room temperature. Tomato plants
were managed by the conventional method using full doses of chemical fertilizers or using
biological inoculants in combination with 25% of recommended P fertilizer. A higher
percentage of fruits were marketable in inoculated plants than that presented in plants
cultivated conventionally after the same storage time.
The efficient operation of the antioxidant enzyme system can result in a better quality
produce with longer shelf life as a result of the maintenance of cellular structure and thereby
the integrity of tissue. The levels of antioxidants such as ascorbate and vitamin E in the fruits
may be indirectly influenced by the expression levels and activity of antioxidant enzymes
such as superoxide dismutase, catalase, and ascorbate peroxidase (Ahn et al., 2002, 2005).
Therefore, AMF could be involved not only in a better P uptake but also in the antioxidant
levels in fruit. This could be an interesting research area to understand the enhanced shelf
life derived from plant AMF inoculation.