White clover seed inoculation and coating in New Zealand

Abstract

This paper reviews the requirement for inoculation of white clover (Trifolium repens) seed with rhizobia bacteria in New Zealand. The pastoral industry relies on the nitrogen fixed by clover's rhizobia bacteria. These rhizobia were not present in soils prior to European settlement, but were introduced as contaminants, and naturally spread with pastoral development. The advent of large scale land development in the 1950s identified areas where clovers failed to nodulate and establish due to the absence of rhizobia, which led to the development of inoculated lime coated seed. Rhizobia have spread widely throughout New Zealand, and in the great majority of situations where pasture is being sown, soils now contain high levels of resident rhizobia capable of nodulating white, red and alsike clover, and inoculation of clover seed is not required. However, it is suggested the use of inoculated clover seed should be considered in the following three situations as an insurance against nodulation failure: undeveloped grasslands with no evidence of resident clover; virgin pastoral land cleared directly from scrub; and paddocks cropped with maize continually for over 10 years. It has been hypothesised that inoculating clover seed may improve clover growth through introducing more effective rhizobia with better nitrogen fixation ability, but the research in this area suggests there is little likelihood of any significant response from doing this. Keywords: rhizobia, inoculation, coated seed, white clover, red clover, alsike clover

High spatial variation in population size and symbiotic performance of Rhizobium leguminosarum bv. trifolii with white clover in New Zealand pasture soils

“…The rhizobia capable of forming root nodule symbiosis with white clover ( Rhizobium leguminosarum bv. trifolii ; Rlt ) were likely introduced into New Zealand on soil and plant material during European settlement in the early 20 th century [ 11 ]. However, occurrences of white clover establishment failure occurred, particularly during large scale pasture development on land cleared of native forest/tussock grassland.…”

Genome sequence of the clover symbiont Rhizobium leguminosarum bv. trifolii strain CC275e

“…Understanding the genetic factors controlling these, and other phenotypes such as saprophytic survival, and desiccation tolerance, will enable increased utilization of R. leguminosarum bv trifolii for farming systems. The strain R. leguminosarum bv trifolii strain CC275e has been commercially used as an inoculant for white-clover for several decades [ 9 ]. The genome sequencing of this ‘highly efficacious’ bacterium, allows for the identification of genetic factors associated with desirable phenotypes (see previous).…”

“…R. leguminosarum bv trifolii strain CC275e is nodule forming (Nod + ) and N 2 fixing (Fix + ) on a range of annual and perennial clover host species. The original isolation of R. leguminosarum bv trifolii strain CC275e was from Trifolium repens L. collected from Montague, North Western Tasmania [ 12 ], and has been used commercially due to its efficacy at forming symbioses and fixation of nitrogen on white clover hosts [ 9 ]. The strain is also moderately effective ( sensu Brockwell et al [ 12 ]) on T. fragiferum L. (strawberry clover; perennial), and T. michelianum Savi , (balansa clover; annual).…”

“…The inoculation of white clover seed with rhizobia commenced in New Zealand in the early 20th century [ 8 ]. In addition to New Zealand produced inoculant strains, R. leguminosarum bv trifolii strain CC275e was sourced from Australia [ 9 ]. From 1974, the inoculant production in New Zealand industry was phased-out and the sole commercial strain for inoculation of white clover seed was strain CC275e, which was then replaced with R. leguminosarum bv trifolii strain TA1 (also from Australia) around 2005.…”

“…Thus, R. leguminosarum bv trifolii strain CC275e was in widespread use in New Zealand for approximately three decades, and is likely to have contributed billions of dollars of nitrogen into New Zealand’s pastoral systems. On white clover, R. leguminosarum bv trifolii strain CC275e has been reported to fix more nitrogen than strain TA1 and has greater persistence in soils [ 9 ]. The decision by the inoculant industry to replace strain CC275e with strain TA1 was based on ease of production.…”