b'Andys Advice:Potato TuberSecond GrowthBy Andy Robinson, Extension Potato Agronomist, NDSU/UMN and Eugenia Banks, Potato Specialist, Ontario Potato BoardThe most common condition leadingtosecondarygrowthisheatstress,specificallysoiltemperatures.Soiltemperatureaslowas75F(24C)can stimulate this disorder, while soiltemperature held at 82 F (28 C) for amonth or 90 F (32 C) for one week Figure 2.have resulted in consistent and signif-icantsecondgrowthoftubers.Thedevelopmentofthissecondgrowthcan also be attributed to other condi-tions that interrupt or temporally haltgrowthsuchasmoisturestressornutrient imbalance. A combination ofPotatotubersaretheresultofthe stresses,suchasheatandmoisture Figure 3.plant genetics and the environmental stress, will exacerbate plant stress andconditions they are grown in. Potato causemorepronouncedsecondvarietiesarecarefullyselectedfor growth. The size, shape, and amounttubers that have high yield and desir- of second growth will depend on theableappearance,tomaximizesales growthstage,variety,andthedura-andreducewaste.However,some tion and intensity of the stress. Thisyears can cause more environmental second growth reduces tuber qualitystress than others, resulting in tuber and reduces marketable yield by con- Figure 4.secondary growth. Secondary growth suming plant energy for heat sproutsoften manifests as heat sprouts, tuber and misshapen unmarketable tubers,chaining,andtubermalformations. while not providing any benefit to theThisphysiologicaldisorderdecreases grower. yield and quality of the tubers in thefield.Inastressfulperiod,normalpotatotubergrowthisinterruptedorstopped,andthennormaltuber Figure 5.growthresumes.Thischangeingrowth can affect how tubers develop. ruption leads to tubers that look likeEarly bulking stress can constrict stem dumbbells(Figure3),kidney-shapedend growth resulting in pointy stem- (Figure 4) or are elongated (Figure 5).end(Figure1)orbottlenecktubers Late-bulkinggrowthdisruptioncan(Figure2).Mid-bulkinggrowthdis- causepointybud-endtubers(FigureFigure 1.12 POTATO GROWER SEPTEMBER/OCTOBER 2020'