Plant breeding for organic and sustainable, low-input agriculture

Nitrogenase activity as the criterion for selection in the red clover breeding
Tomas Simon 1 , Hana Jakesova 2
1 Crop Research Institute, Prague, Czech Republic
2 CSc., Red Clover, Grass Breeding, Hladke Zivotice, Czech Republic
Low-input agriculture which becomes a common farming practice needs the perennial forage
legumes such as clover that markedly contribute to the soil nitrogen balance through effective N2
fixation. Improving N2 fixation by means of selection and breeding reduce reliance on soil and N
fertilizers, whilst enhancing residual benefits to subsequent crops.
Hydroponic perlite culture as the cultivation environment enabling to eliminate soil N was used
for screening of 4000 individual plants obtained from previous cycles of recurrent breeding for
enhanced nitrogenase activity. Plants were inoculated with effective Rhizobium leguminosarum
bv. trifolii strain. Total nitrogenase activity (TNA) (µmol/plant/hour) was measured at the onset
of flowering and root volume (ml/plant) and forage matter (fresh and dry) (g/plant) were
determined. Water soluble carbohydrates content (WSC) was determined in dry forage matter
using both liquid chromatography and NIR spectrometry. 360 of them were selected according to
TNA and planted to the nursery in 2003. Forty plants within the nursery were selected for open
pollination according to the health status, vigour, size of plant, seed harvest etc. in the summer
2004. Consequently fourteen individual plants with extremely high nitrogenase activity and very
good agronomical value were selected after seed harvest. Their seed progenies (1008 plants in
total) were screened in the second experiment (2005) and plant characteristics were determined
as described above. Intraclass correlation coefficients (h 2 ) were calculated for parents and
progenies as an estimate of heritability and relationships among determined characteristics were
assessed for both the populations.
Heritability estimate for TNA was more than six times higher in progenies screened in the
second experiment (h 2 =0.4645) that those for parents from the first experiment (h 2 =0.0739).
Increased h 2 was observed also for root volume (3.24 times) for progenies compared to the
parents. On the other hand, selection for high nitrogenase activity did not affect the heritability
estimates for forage yield. Selection for enhanced nitrogenase activity resulted in increased
number of above-average plants in progenies screened in the second experiment (by 8.8% for
TNA; 3.5% for root volume and 5.0% for dry forage matter) compared to the parents from the
first experiment. Total nitrogenase activity was significantly positively correlated with root
volume, fresh forage and dry forage (p