Can internal rust spot in potato tuber be prevented by agronomic practices ?
W. Reust, J.-P. Dutoit
Swiss federal research station for plant production, Case postale 254, CH-1260 Nyon 1, Switzerland
Keywords: Internal rust spot, fertilization, calcium, variety, quality
Introduction
Internal rust or brown spot (IRS) may have different origins as viruses or as in our case a physiological disorder of tubers. It is characterized by the occurrence of irregular shaped reddish-brown lesions in the tuber. Several hypothesis for the development have been put forward, some authors have suggested that nutrient imbalance is the main causative factor and particularly calcium uptake and transport to the developing tubers. The resulted deficiency can be exacerbated by poor calcium and irregular water supply, soil type and temperature, rapid tuber bulking and variety choice (Davies and Ross, 1986). These damages reduce largely tuber quality and can provoke important income losses to farmer.
In most cases susceptible varieties are rejected and not admitted to the variety list. However some exception may occur with high specific quality cultivar. Trials on cropping techniques with the objective to prevent the disorder have been done.
Materials and methods
From 1999 to 2001 several trials took place on two farms of our Institute with the processing variety Santana (french frites) sensitive to IRS in our production condition as earlier experimentation showed.
Trials included early and later planting times, analysis of the bulking rate and dry matter accumulation, irrigation, additional soil and foliage fertilization with calcium.
Results
Growth and bulking rate analysis showed that IRS appears in tuber flesh as early as after 100 vegetation days and increased in percentage as well in the severity of the damage (index) up to more than 25% of the tubers. The potential yield of the variety is generally reached in 115 to 125 days after planting (Fig. 1).
Early planting developed significantly more IRS than late planting
with nearly similar growth duration. Irrigation of the crop increased yield by 25% and IRS by more than 20%. Foliage application of CaCl2 and CaO had no reduction effect.
These results showed clearly the susceptibility of this variety and any avoiding with complementary fertilization is totally uncertain.
0 50 100 150 200 250 300 350 400 450 500
65 75 85 95 105 115 125 135
Days after planting
Yield dt/ha
8 9 10 11 12 13 14 15 16 17 18
> 70 mm 50-70 mm 35-50 mm
< 35 mm
% Starch
% Starch
0 5 10 15 20 25
65 75 85 95 105 115 125 135
%
0 10 20 30 40 50 60 70 80
Index
% Index
Proceedings of Triennal Conference of the EAPR, July 14-19, 2002, Hamburg (D),136
References
DAVIES H.V, and ROSS H.A. 1986. The development of internal rust spot in potato tubers. Aspects of Applied Biology13,433-435.
Fig.1. Internal rust spot in tuber
Fig.2. Yield, dry matter and IRS increase during the growing period
