Border cell counts of Bollgard3 cotton and extracellular DNA expression levels

In a world where there is growing pressure to grow more with a smaller environmental footprint, alternative forms of plant protection are needed. The root tips of most plants produce border cells in a mucilage that also contains extracellular DNA (exDNA), which is known to be involved in plant defence. A decade after we first demonstrated that there was varietal difference in the number of border cells in Australian cotton cultivars, we enumerated current commercial cultivars and assessed the level of exDNA produced by individual root tips. The results exposed that there has been a change in the number of border cells per root tip, that cultivar variation still exists and that the recovered levels of exDNA also differs. However, there was no correlation between border cell number and disease resistance to two of the major wilt pathogens and the levels of exDNA did not change when a root tip suspension was incubated with spores of fungal pathogens. The results imply that, while there is potential for border cells and root tip properties to be incorporated into breeding programmes, we still need to develop a better understanding of how root tips are able to influence disease epidemiology if we are to capitalise on this phenotypic property.