Plant growth-promoting rhizobacteria (PGPR) colonize root hairs and lateral roots and provide nutrients and water to the plants and in return the plants produce and give back sugars. Not only do the microbes give nutrients, they also produce growth-promoting hormones which can stimulate root elongation and lateral root growth. What does this mean for the giant pumpkin grower? More roots and bigger roots and possibly a bigger pumpkin as a result. Microbes can also produce hormones that help the plants deal with things like drought stress better and help protect the plants from pathogens.
So, what types of bacteria and fungi can have the best overall affects for your plant? I think scientist would agree that this is an emerging field of study with not enough research to draw any solid conclusions. For my pumpkin patch, I'll be using RAW Microbes (different strains of mycorrhizae and bacillus), Biota Max (different strains of bacillus and trichoderma), Actinovate, Azos and WOW mycorrhizae. There are other items I would like to add to this mix (namely Rootshield and Companion), but at some point you have to draw a line when it comes to costs and some of those patented biologicals can be pretty pricey. Although the research says they are good.
One new thing I found out this week when doing some research is that there are three different types of Azos (amazonense, brasilense, and lipoferum). This was something I wasn't aware of. Azos is listed as a nitrogen fixing bacteria, which is true, but I think it is the less interesting aspect of the bacteria. The more interesting part of Azos is the growth promoting hormones (IAA) that are produced on the roots, which can increaes the root mass. All three types of Azos have been found to be effective. But each of the three have characteristics that are unique to them.
Azospirillum amazonense seems to do better in lower pH soils. Azospirillum brasilense is the most well studied. It is best known for helping plants use carbohydrates. Azospirillum lipoferum is set apart from the others for elongating the roots in plants more than the other species. In the past I've used Azospirillum brasilense on my plants. This year I'm trying Azospirillum lipoferum. I doubt I'll be able to find an big difference between the two, so this decision is more economic than anything else, but better root elongation sounds good to me.