About The Key

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Sweetpotato Diagnotes is a Lucid3 interactive matrix key.  In a matrix key, users may answer any question in any order, and each selection has the potential to reduce the number of possible causes.  In a traditional dichotomous key, questions must be answered in a specific order, each answer dictating which question comes next.  If the user does not have the information to answer a question, the diagnosis can not proceed.  This is often the case in diagnosing a crop problem, as symptoms or signs may vary with the stage of the crop or the stage of the problem development, and among the different parts of the crop.  Only some of the symptoms may be available to the user in a specimen provided by a farmer.  Using a matrix key, any information available may be used to shorten the list of possibilities.

How to use the key:

The screen layout


When you open the key, four windows are displayed.  The top left window contains the questions. To see the options, click on the + symbol beside the question.  Select the options by clicking in the empty box beside them.  Your selection will appear in the lower left window, which keeps a record of your choices.  When you have finished with that question, click the - symbol to hide the choices.  This will often save you having to scroll down to the bottom of the window to find more questions.

In the top right-hand window is a list of all the possible problem causes that are contained in the key.  By choosing answers to the questions, some entities will be discarded from this list.  The discarded entities are displayed in the lower right-hand window.  The aim is to reduce the number of possible causes in the top window to one or a few.

Click the picture to enlarge if not clear on your screen.

The process

Initially the top window contains only a short list of questions.  These are questions which generally apply to all users.  Other questions are hidden.  Depending on which options you choose, the questions most relevant to you will appear.  In this way, the key operates somewhat like a pathway key, except that you may follow several different pathways to the same diagnosis, depending on the appearance of symptoms in a particular case.

  • You don't have to answer all the questions, and it doesn't matter what order you answer them in.  If several new questions are offered, skip to the question that seems most relevant to you.  If you don't think any of the options fits your case, skip the question.  If you run out of questions, you may want to come back to the ones you missed.

  • You can choose more than one answer to one question.  Often it is a combination of features which defines a particular problem.  The options may be worded to cover both general and more specific features, or they may cover different aspects, for example colour and distribution.  Select all the options that apply to your specimen.  For example, if the main problem is rot in storage roots, but there are also fungal structures present, select options for both rot and fungal structures.


    However, beware that your specimen may have symptoms of more than one problem present.  It is best to key different symptoms separately at first, unless you are sure they are related.  When you have gone as far as you can with one symptom but you still have a number of possible causes, go back and make selections relating to any other symptoms that might be related.

  • You can undo a selection.  Just click the ticked box again, in either of the left-hand windows.

  • Keep selecting options until you have only one problem cause remaining, or until you run out of questions.  If only a few problem causes remain, view the fact sheets for each cause.  If there are more than a few, look back over the key to see if there are additional questions you could answer, or additional options you could choose. Alternatively, try the "calculate differences" tool at the right-hand end of the tool bar.  This gives a list of all the questions where scores for the remaining causes differ.  Click a question, and the options scored for each remaining cause will be displayed. 

  • If you end up with no problem causes remaining, look back over your selections, and undo any you were not sure about, or which don't seem essential to describe the specimen. 

    If you have answered questions relating to more than one type of symptom that is present, focus on one symptom and remove choices relating to the other.  Also, try undoing your answer to "Where is the crop?"  It is possible that some causes are more widely distributed than published information suggests.

  • You can restart the key, using the icon at the left-hand end of the tool bar.

  • You can change the size of the windows by dragging their inside edges.  You may want to make the left window wider, to read the longer options without having to scroll across.  You can drag it back again when you need to read the full names of remaining problem causes.

  • You can choose to see all the questions but the key must be restarted (you will loose selections made). In the "Key" menu, select "Dependency Mode" and click on "Positive Dependencies" to turn them off.

The media

Items in the key can have pictures or html pages attached to them.  They are displayed as an icon to the left of the item.  Clicking the icon will open the attached page.  The media may help to illustrate or explain the option.  However, be aware that the photo displayed is only one example of what might be a diverse range of symptoms covered by a particular option.


Every problem cause has a Fact Sheet attached.  When you have reduced the list of causes remaining to one or a few, view the fact sheet for each remaining cause to see photos and additional information that will help you decide if this is the likely cause of your problem.