Interactions of Tylenchulus semipenetrans infection, soil salinity, and citrus rootstocks

228 Pages·1992·7.6 MB·English

by  Mashela, William Phatu

INTERACTIONS OF TYLENCHULUS SEMIPENETRANS INFECTION
SOIL SALINITY, AND CITRUS ROOTSTOCKS
By
WILLIAM PHATU MASHELA
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1992
For all the South African Einsteins who are being denied
an opportunity to discover relativity.
ACKNOWLEDGEMENTS
Critical evaluationsbyAssociate ProfessorL. W. Duncan,
Professor R. McSorley, and Professor J. P. Syvertsen of the
proposal leading to this research, greatly reduced the
stresses of interpreting data from experiments with erroneous
designs. Although the author led every aspect of this
endeavor, the guidance in formulating the precise guestions
was indispensable. Profound indebtedness is reserved for the
chairperson, Dr. Duncan, and cochair, Professor McSorley, for
the rigorous training in scientific writing and scholarly
presentation of scientific work. Also, the author expresses
profound gratitude to Dr. Duncan for financing the project,
for personally assisting during field studies, for allowing
technical assistance, especially incarbohydrateanalysis, and
for instructions in specialized areas of nematology.
The author is profoundly grateful to Professor J. P.
O'Bannon, who suggested reciprocal interactions of salinity
and nematodes as a possible dissertation area, and for the
many generous hours he accorded the author in terms of
discussions during the inception phase. Professor Syvertsen
played an indispensable role as chair of the author's minor.
Heprovided eguipment, pertinent literature, andprudent ideas
on mechanistic studies, and also instructed the author on
.
various aspects of salinity and plant physiology. Professor
J. H. Graham accorded invaluable advises on cultural
practices, technical problems, and on conditions by which
salinity increases population densities of the citrus
nematode
Genuine thankfulness is also due to Denise Dunn for
analyzing carbohydrates, for instruction in this area, and
above all, for the friendship. Fervent appreciation is also
due to Martin Smith for instructions in CI analysis and
photosynthesis measurements. The author also thanks Mary
Ahnger for preparing figures for this study and instruction in
computers. Other members of the faculty, particularly
Professors G. Albrigo, B. L. McNeal, and G. C. Smart Jr., are
acknowledged forinstructions incitriculture, soil chemistry,
and nematology, respectively. Felsmere Co. provided an
orchard where the effects of nematodes on mature trees were
studied; whereas the effects of nematodes on replants were
studied on Dr. J. W. Noling's experimental plots. All these
individuals, alone or combined, will forever be held in
highest esteem.
Finally, the author thanks his family, the family that he
has always wanted to be his family.
iv
TABLE OF CONTENTS
ACKNOWLEDGEMENTS 111
LIST OF TABLES vii
LIST OF FIGURES xii
ABSTRACT xiii
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. REVIEW OF LITERATURE 5
Introduction
MTSevacllheiannnciihtcuyalluisnrocsoiettmriuppsreunnepitrnrogadnusction !."!!! 315955
CHAPTER 3. LEACHING SOLUBLE SALTS INCREASES POPULATION
DENSITIES OF TYLENCHULUS SEMIPENETRANS 44
MIantterroidaulcstioannd Methods 4445
Results
Discussion ][ 4586
CHAPTER 4. SALINITY REDUCES RESISTANCE TO TYLENCHULUS
SEMIPENETRANS IN CITRUS ROOTSTOCK SEEDLINGS ... 59
Introduction
Materials and Methods 5690
Results
Discussion ] 63
69
CHAPTER 5. TYLENCHULUS SEMIPENETRANS REDUCES SALT
TOLERANCE IN CITRUS ROOTSTOCK SEEDLINGS 72
Introduction
Materials and Methods 7732
Results
Discussion . ]* 87g7
v
CHAPTER 6. TYLENCHULUS SEMIPENETRANS INCREASES FOLIAR
CHLORIDE AND SODIUM, BUT DECREASES NUTRIENT IONS IN
CITRUS REPLANTS AND MATURE TREES 94
Introduction 94
Materials and Methods 96
Results 99
Discussion 106
CHAPTER 7. SALINITY INCREASES TYLENCHULUS SEMIPENETRANS
DENSITIES THROUGH SYSTEMIC EFFECTS, BUT THE
NEMATODE INCREASES CHLORIDE AND SODIUM IN CITRUS
LEAVES THROUGH NONSYSTEMIC EFFECTS 110
Introduction 110
Materials and Methods 112
Results 115
Discussion 119
CHAPTER 8. MECHANICALROOT PRUNING SIMULATES THE EFFECTS
OF TYLENCHULUS SEMIPENETRANS ON OSMOTICUM IONS AND
STARCH IN CITRUS 125
Introduction 125
Materials and Methods 126
Results 129
Discussion 135
CHAPTER 9. OSMOTIC POTENTIAL, OSMOTICUM IONS,
TRANSPIRATION, AND C0 ASSIMILATION IN SOUR ORANGE
SEEDLINGS AS AFFECTED2BY TYLENCHULUS SEMIPENETRANS
AND MECHANICAL ROOT PRUNING 141
Introduction 141
Materials and Methods 142
Results 146
Discussion 153
CHAPTER 10. SUMMARY AND CONCLUSIONS 158
APPENDICES. NONOSMOTICUM IONS 164
REFERENCE LIST 183
BIOGRAPHICAL SKETCH 212
vi
,,,
LIST OF TABLES
TABLE 3-1. Tvlenchulus semipenetrans female counts per
gram of fresh roots on salt-tolerant Rangpur lime
as affected by soil type, discontinuous salt,
continuous salt, or no salt treatments 50
TABLE 3-2. Tvlenchulus semipenetrans egg counts per
gram fresh roots on salt-tolerant Rangpur lime as
affected by soil type, discontinuous salt,
continuous salt, or no salt treatments 51
TABLE 3-3. Fecundity of Tvlenchulus semipenetrans
females per gram fresh roots on salt-tolerant
Rangpur lime as affected by soil type,
discontinuous salt, continuous salt, or no salt
treatments 52
TABLE 3-4. Osmotic potential (tt) and pH of soil
leachate as affected by soil type (loamy sand,
organic mix, sand) and discontinuous salt (DS)
continuous salt (CS), or no salt (NS) treatments. 53
TABLE 3-5. Tvlenchulus semipenetrans female and egg
counts per gram of fresh roots on salt-sensitive
Sweet lime as affected by discontinuous salt (DS)
continuous salt (CS), or no salt (NS) treatments.
54
TABLE 3-6. Osmotic potential (w) and pH of soil
leachate, and leaf chloride (CI) of Sweet lime as
affected by soil type (loamy sand, organic mix,
s(aCnS)d), oarndnodisscalotnti(nNuS)oustresaatlmten(tDsS), continuous salt 55
TABLE 4-1. Tvlenchulus semipenetrans female counts per
gram of fresh roots 8 weeks after inoculations of
hsiugshcleyptriebsliestan(tS)(R),cimtorduesraterloyotrsetsoicsktantse(eM)dl,inagnsd
previously grown with and without salinity. ... 64
TABLE 4-2. Tvlenchulus semipenetrans juvenile counts
per gram of fresh roots 8 weeks after inoculations
of highly resistant (R), moderately resistant (M)
vii
and susceptible (S) citrus rootstock seedlings
previously grown with and without salinity. . . . 65
TABLE 4-3. Tylenchulus semipenetrans egg counts per
gram of fresh roots 8 weeks after inoculations of
hpsirugeshvclieyoputrsielbsyliesgtraonw(tnS)w(Ri)t,hcimtaorndudesrwaittehrlooyuottrsetssoaiclsiktnainttys.e(eM)dl.,i.nagn.sd 66
TABLE 4-4. Fecundity (number of eggs/female) of
Tylenchulus semipenetrans females 8 weeks after
rsieenseoidcsluitlnaagntstion(sMp)r,eofvainodhuissgluhyslcyepgrtreiosbwilnseta(nwSti)thc(iRt)ra,unsdmordoeworitatsthteoolucytk
salinity 67
TABLE 4-5. Root and shoot weights (g) of 9-month-old
hsiugshcleyptriebsliesta(Sn)t (cRi)t,rumsoderroaottesltyocrkesisseteadnlting(Ms),thaantd
were exposed to a 3-week salt treatment (salt) or
not exposed (control) when 6 months old and then
inoculated with Tylenchulus semipenetrans when 7
months old 68
TABLE 5-1. Concentrations (% weight) of chloride in
leaves of highly salt-tolerant (H) moderately
sseaeldtl-itnogleruanndter(Mn)o,nsaalnidnistaylta-nsdensliotwivse,ali(nS)ityciwtirtush
and without Tylenchulus semipenetrans infection 4
weeks after salinity 78
TABLE 5-2. Concentrations (% weight) of chloride in
trsooeoletedsrlaionnftghuing(dMh)elry, snaoalnntsd-atloislnaeilrttay-nstaenn(dsH)itl,iomvweodsearl(aiSt)neiltyyciswtairltutsh-
and without Tylenchulus semipenetrans infection 4
weeks after salinity 79
TABLE 5-3. Concentrations (% weight) of sodium in
ssleaeaelvdtel-sitnogloefruanndhteirg(hMln)yo,nsasanaldlitn-ittsoyalletar-nasdnetnlsoiw(tHi)vs,ealim(nSo)idteyrcaiwttiertulshy
and without Tylenchulus semipenetrans infection 4
weeks after salinity 80
TABLE 5-4. Concentrations (% weight) of sodium in roots
tosfoeleedrhlaiinngtghlyun(Md)sea,rltn-aontndoslaelriannsitatlyt-(asH)nedn,siltmoiowvdeesraalt(ieSn)liytyciswtariluttsh-
and without Tylenchulus semipenetrans infection 4
weeks after salinity 81
vm
TABLE 5-5. Concentrations (% weight) of potassium in
ssleaeaelvdtel-sitnogloefruanndhteirgh(Mln)yo,nssaaalnlidtn-isttaoylltea-rnsadenntsliotw(iH)vse,alim(nSo)idteyrcaitwteirltusyh
and without Tylenchulus semipenetrans infection 4
weeks after salinity 82
TABLE 5-6. Concentrations (% weight) of potassium in
trsooeloetedsrlaionnftghuing(dMh)elry, snaoalnntsd-atloislnaeilrttay-nstaenn(dsH)itl,iomvweodsearl(aSit)neiltyyciswtairltuts-h
and without Tylenchulus semipenetrans infection 4
weeks after salinity 83
TABLE 5-7. Concentrations (% weight) of starch in roots
tosfoeleedrhlaiinngtghlyun(dMs)ear,ltn-oatnnosdlaelriasnnaitltty-s(aHe)nnds,itlmioovwdeesraal(tSie)nliytyciswtairltuts-h
and without Tylenchulus semipenetrans infection 4
weeks after salinity 84
TABLE 5-8. Concentrations (% weight) of ketone sugars
ssineaeldtrl-oitonotglseruoanfndtehri(gMnh)ol,nysaaslnaidlntis-tatylotla-ensrdeannstliotw(iHv)sea,li(mSno)idteyrcaitwteriultsyh
and without Tylenchulus semipenetrans infection 4
weeks after salinity 85
TABLE 5-9. Mean shoot and root weights (g) of highly
asnadlt-toslaelrta-nstens(Hi)ti,vemod(eSr)atecliytrussalts-eteodlleirnagntun(dM)er,
nonsalinity and low salinity with and without
Tylenchulus semipenetrans infection 4 weeks after
salinity 86
TABLE 5-10. Tylenchulus semipenetrans on highly salt-
tsoalletr-asnetnsi(tHi)v,e mod(eSr)atelcyitsraulst-tosleeerdalnitng(M),undaenrd
nonsalinity and low salinity 4 weeks after
salinity 87
TABLE 6-1. Soil characteristics of citrus replant plots
in south central Florida and of an orchard with
mature trees in the eastern coast of Florida with
trees infested with low and high densities of
Tylenchulus semipenetrans 100
TABLE 6-2. Foliar concentrations of four macronutrients
(% dry weight) and three micronutrients (ppm dry
weight) in citrus replants with low and high
densities of Tylenchulus semipenetrans (per 100 cm3
soil) 10i
ix
TABLE 6-3. Concentrations (% dry weight) of leaf
osmoticum ions in mature citrus trees with low and
high densities of Tvlenchulus semipenetrans (per
100 cm3) 102
TABLE 7-1. Tvlenchulus semipenetrans (T) female,
juvenile, and egg counts per gram of fresh roots of
sour orange seedlings with split-roots treated with
(S) and without (0) low salinity 116
TABLE 7-2. Spatial effects of Tvlenchulus semipenetrans
(T) with (S) and without (0) low salinity on foliar
osmoticum ions (% dry weight) of sour orange
seedlings with split-roots 117
TABLE 7-3. The partitioning of the concentrations (%)
pooftassstiaurmch(K), icnhlotrwioderoo(tCI)ha,lvessodiausmaf(fNeac)t,edabnyd
Tvlenchulus semipenetrans infecting half-root
system of sour orange seedlings with split-roots . 117
TABLE 7-4. Effects of Tvlenchulus semipenetrans (T) and
salinity (S) separated or combined on dry shoot and
root weights and shoot height of sour orange with
split-roots 118
TABLE 8-1. Concentrations of root carbohydrate (% dry
weight) of Cleopatra mandarin seedlings as affected
by root pruning and Tvlenchulus semipenetrans
infection with and without low salinity 130
TABLE 8-2. Concentrations (% dry weight) of leaf and
root osmoticum ions in Cleopatra mandarin seedlings
as affected by root pruning and Tvlenchulus
semipenetrans infection with and without low
salinity 131
TABLE 8-3. Concentrations (% dry weight) of leaf and
root osmoticum ions in sour orange seedlings as
affected by root pruning and Tvlenchulus
semipenetrans infection with and without low
salinity 132
TABLEma8n-4d.arinDryansdhoostouarndorroaontgeweiagshtsaff(ge)ctoefdClbeyopartoroat
pruning and Tvlenchulus semipenetrans infection
with and without low salinity 133
TABLE 8-5. Tvlenchulus semipenetrans per gram fresh
root weight of Cleopatra mandarin and sour orange
growing grown with and without salinity 134
x