On the trial of fast growing direct drilled wheat roots by Michelle Watt, Margaret McCully and lohn Kirkegaard CSIRO Plant Industry

Fast and slow growing wheat roots. Left: Tip was growing quickly, indicated by the smooth, clean appearance. Right: Distorted tip was growing slowly due to soil properties. Direct-drilled wheat has more slow roots because of the soil structure.

GROWTH OF direct-drilled ('no-till') wheat seedlings is influenced by soil structure, soil biology and wheat genotype. If the soil is cultivated (loosening the soil and removing biopores), shoot growth can improve. If the soil is fumigated (killing soil biota), shoot growth can also improve.

The challenge is to determine exactly why this occurs and how to get around structural and biological constraints. Breeding for fast-growing wheat roots may be one promising avenue.

A major portion of the biological constraint is known to be a group of toxin-producing bacteria called Pseudomonads.

Wheat varieties differ in seedling vigour when direct-drilled. We have compared variety Janz and a CSTRO line bred for high seedling vigour in no-ti ll and cultivated soil. The high vigour wheat roots grew 40 per cent faster than those of Janz in no-till soil and produced more biomass.

Slow-growing roots allow bacteria to collect around their tips. Microscopy and microbiology showed many more bacteria, including the Pseudomonads, on slowgrowing root tips compared to fast-growing tips.

The superior performance of the high vigour wheat in no-till soil may be because their vigorous, fast-growing roots outpace colonisation by toxic microbes by overcoming constraints of soil compaction and biopore entrapment.

Microscopy has shown us that in minimum-tilled paddocks, in a wheat-canola rotation , residues of the roots from both crops remain in the numerous old root channels for up to two seasons while these are colonised by roots of the subsequent crops. The living roots mingle intimately with the old root residues, possibly utilising the nutrients released from them by microbes in the pores. Young roots, however, may become trapped in pores, slowing their growth.

Four wheat roots in a biopore, intimately associated with each other and the residue of a canola root from the previous crop in the background. Roots anchored to the edges of the pore by root hairs.

Region North, South, West