Winter Yellows - A closer look at this physiological disorder and other issues Sandra Hardy, NSW DPI Pat Barkley, ACG
Outline Winter Yellows: Typical symptoms What we know Previous instances Reasons why? Weather patterns Carbohydrates -leaves -roots Summary Other issues PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Typical symptoms Yellowing of leaves leaves stay yellow throughout winter Autumn Usually latest flush affected Younger trees (2-5yrs) little/no crop PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Other symptoms include. Sometimes: whole tree affected leaf fall out-of-season flowering Spring recovery PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Previous work After 1952-1954 1954 outbreaks Affected leaves: low in calcium (1-2%, 3.5-4.5% in healthy leaves) high in starch Roots - starch depleted death smallest roots 1st Applying N aggravated symptoms PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Previous recorded occurrences - MIA Plant disease surveys 1952-1986 1953 widespread (+ coast & lower Murray) 1955 young trees 1956 & 1963 scattered trees, mild symptoms 1973 severe (+ Narromine) 1977- young blocks 2005 widespread 2008 - widespread
50 45 40 35 30 25 20 15 10 5 0 1952 weather Griffith Weather Data 1952 1-Jan-52 15-Jan-52 29-Jan-52 12-Feb-52 26-Feb-52 11-Mar-52 25-Mar-52 8-Apr-52 22-Apr-52 6-May-52 20-May-52 Date 30 25 20 15 10 5 0 Temperature (oc) Rainfall (mm) Series2 Series1 Series3
45 40 35 30 25 20 15 10 5 0 1953 weather - WY Griffith Weather Data 1953 1-Jan-53 15-Jan-53 29-Jan-53 12-Feb-53 26-Feb-53 12-Mar-53 26-Mar-53 9-Apr-53 23-Apr-53 7-May-53 21-May-53 Date 30 25 20 15 10 5 0 Temperature (oc) Rainfall (mm) Max Min Rainfall
45 40 35 30 25 20 15 10 5 0 2007 weather Griffith Weather Data 2007 1-Jan-07 15-Jan-07 29-Jan-07 12-Feb-07 26-Feb-07 12-Mar-07 26-Mar-07 9-Apr-07 23-Apr-07 7-May-07 21-May-07 Date 25 20 15 10 5 0 Temperature (oc) Rainfall (mm) Temp Max Temp Min Rainfall
45 40 35 30 25 20 15 10 5 0 2008 weather - WY Griffith Weather Data2008 1-Jan-08 15-Jan-08 29-Jan-08 12-Feb-08 26-Feb-08 11-Mar-08 25-Mar-08 8-Apr-08 22-Apr-08 6-May-08 20-May-08 Date 30 25 20 15 10 5 0 Temperature (oc) Rainfall (mm) Max Min Rainfall
Climatic triggers? Good summer rainfall Sudden cold snaps in early-mid autumn
Carbohydrates (CHO) Solar energy stored as chemical energy in form of CHO & other compounds Leaves manufacture CHO Accumulated: leaves (1 st ), branches, trunks, roots (last) Tree CHO levels variable: seasonal demands of competing developing vegetative & reproductive sinks Starch main CHO
CHO - sinks & storage Actively growing organs strong/priority SINKS Storage: roots (highest) > leaves/branches > trunk (lowest) Allocation to storage lower priority than needs of actively organs
CHO sinks & storage Reserves affect flowering, fruit set and yield following year Large crop loads (e.g. on year ): depletes CHO severe tree collapses/dies e.g. Murcott reduces summer/autumn flush CHO accumulation: most rapid between 5 15 C affects photosynthesis/cho transport
Leaves Long lived: 2+yrs if N adequate Photosynthesis rates relatively low Photosynthesis optimum 25-30 C, reduced - at high temps >35 C & low temps Up to 45% dry matter mostly cell walls complex CHO
Leaves & CHO Age affects CHO storage & export No CHO export until FULLY expanded (1-2mths) Significant importer prior to export New flush strong sink
Leaves & CHO Older/shaded leaves export greater portion of CHO & more rapidly Shaded leaves significant contributor to autumn & winter CHO reserves Starch not readily mobilised for export No sinks chloroplasts packed with starch cell membrane damage
Movement of carbohydrates Fruit source CHO principally from leaves of same growth cycle (Source: Goldschmidt & Koch, adapted from Powell & Krezdorn 1977)
3 factors: - shoot growth* - soil temperature -soil water Root growth Growth alternates with shoot growth - greatest when shoots not growing * Major factor controlling intensity of root growth PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Root growth Valencia on Rough lemon Valencia on Carrizo citrange Source: Bevington & Castle 1985.
Root growth temperature & water Soil temperature: most intense at > 27 C limited < 22 C none below 14 C Soil water: Little growth < - 50 kpa (-0.05MPa) PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Roots & CHO reserves Highest CHO reserves usually in root Starch accumulation in roots mostly autumn & winter - dependent fruit/vegetative flush demands Build up greatest in absence of veg/fruit sinks (e.g. off year) C depletion high under a heavy crop load PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
Summary - why leaves turn yellow Latest leaf flush able to produce CHO but can t export (leaves too young) + also a sink for CHO If no/little fruit no sink competition for CHO flush CHO movement to roots restricted Sudden low temperatures photosynthesis slows + CHO accumulates So..
Summary - why leaves turn yellow Youngest leaf flush loaded with starch normally re-greens following spring Severe - permanent damage to leaf structure Roots starved of CHO die
Reducing impact of winter yellows on young trees Avoid promoting vigorous autumn flush Leave some fruit on
Other reasons for leaf yellowing PRESENTATION TITLE --- NAME, POSITION TITLE.GO TO VIEW, MASTER, SLIDE MASTER
root curling Don t plant root-bound trees Check young tree roots before planting
Other reasons for leaf yellowing
root death Choose soil type carefully Manage irrigation to avoid over watering
Other contributors to tree collapse
collar rot Remove/check tree guards
References Bevington,K.B. and Castle,W.S. Annual root growth patterns of young citrus trees in relation to shoot growth, soil temperature and soil water content. 1985. J.Amer.Soc. Hort. Sci. 110 (6): 840-845. Cameron, S.H. Starch in young orange tree. American Soc. for Horticultural Science. Pp 110-114. Castle,W. S. 1978. Citrus root systems: their structure, function, growth and relationship to tree performance. Proc.Int.Soc.Citriculture. 62-69. Fraser, L.R. and Barkley,P. Virus and related diseases of citrus in New South Wales. Dept. of Agriculture,NSW. Goldschmidt,E.E. and Koch,K.E. 1996. Citrus in Photoassimilate distribution in Plants and Crops Source-sink relationships. Ed. E.Zamski and A.A.Schaffer.pp 797-823 Goldschmidt, E.E. 1999. Carbohydrate supply as a critical factor for citrus fruit development and Productivity. HortScience, Vol34(6) October. pp. 10201024 Lenz,F. 1978. Photosynthesis and respiration of citrus as dependent upon fruit load. Proc.Int.Soc.Citriculture. pp 70-71 Purvis,A.C. and Yelenosky,G. 1983. Translocation of carbohydrates and proline in young grapefruit trees at low temperatures. Plant Physiol 73, pp877-880. Schaffer,A.A; Liu,K.; Goldschmidt,E.E.; Boyer,C.D. and Goren,R. 1986. Citrus leaf chlorosis induced by sink removal: startch,nitrogen and chloroplast ultrastructure. Plant.Physiol. 124: 111-121. Syvertsen,J.P. and Lloyd,J.J. 1994. Citrus in Handbook of environmental physiology of fruit crops. Vol 2 Subtropical and tropical crops. Ed. B.Schaffer and P.C.Anderson. Pp65-99. Vu,J.C. Photosynthetic responses of citrus to environmental change. In Handbook of Plant and Crop Stress. Ed M. Pessarakli. Pp 947-961 Yelonosky,G. and Guy,C.L. 1977. Carbohydrate accumulation in leaves and stems of Valencia orange at progressively colder temperature. Botanical Gazette 138 (1): 13-17